I'm trying to test some glibc.spec fixes. To test those modifications it is necessary to rebuild glibc package and during this I found tant building glibc fails on my system in %check because by default compile time warnings are treated as errors.
Of course I was able to continue building my new version of the glibs by add --without werrors to rpmbuild parameters however looks like some recent gcc updates started reporting some new warnings.

Part of the build log:

gcc /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-cos.c -c -std=gnu11 -fgnu89-inline  -O3 -Wall -Werror -Wundef -Wwrite-strings -fasynchronous-unwind-tables -fmerge-all-constants -fno-asynchronous-unwind-tables -frounding-math -fstack-protector-strong -g -mtune=generic -Wstrict-prototypes -Wold-style-definition       -fno-builtin -D__FAST_MATH__ -DTEST_FAST_MATH -fno-inline -ffloat-store -D_OPENMP=201307 -Wno-unknown-pragmas    -D__NO_MATH_INLINES -D__LIBC_INTERNAL_MATH_INLINES -I../include -I/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math  -I/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux  -I../sysdeps/unix/sysv/linux/x86_64/64  -I../sysdeps/unix/sysv/linux/x86_64  -I../sysdeps/unix/sysv/linux/x86  -I../sysdeps/unix/sysv/linux/wordsize-64  -I../sysdeps/x86_64/nptl  -I../sysdeps/unix/sysv/linux/include -I../sysdeps/unix/sysv/linux  -I../sysdeps/nptl  -I../sysdeps/pthread  -I../sysdeps/gnu  -I../sysdeps/unix/inet  -I../sysdeps/unix/sysv  -I../sysdeps/unix/x86_64  -I../sysdeps/unix  -I../sysdeps/posix  -I../sysdeps/x86_64/64  -I../sysdeps/x86_64/fpu/multiarch  -I../sysdeps/x86_64/fpu  -I../sysdeps/x86/fpu/include -I../sysdeps/x86/fpu  -I../sysdeps/x86_64/multiarch  -I../sysdeps/x86_64  -I../sysdeps/x86  -I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96  -I../sysdeps/ieee754/dbl-64/wordsize-64  -I../sysdeps/ieee754/dbl-64  -I../sysdeps/ieee754/flt-32  -I../sysdeps/wordsize-64  -I../sysdeps/ieee754  -I../sysdeps/generic  -I.. -I../libio -I. -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -isystem /usr/include  -D_LIBC_REENTRANT -include /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/libc-modules.h -DMODULE_NAME=nonlib -include ../include/libc-symbols.h       -DTOP_NAMESPACE=glibc -o /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-cos.o -MD -MP -MF /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-cos.o.dt -MT /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-cos.o
../sysdeps/x86_64/fpu/test-double-vlen2-wrappers.c: In function 'sincos_vlen2':
../sysdeps/x86_64/fpu/test-double-vlen2-wrappers.c:33:46: error: 'mr1' is used uninitialized in this function [-Werror=uninitialized]
 VECTOR_WRAPPER_fFF_2 (WRAPPER_NAME (sincos), _ZGVbN2vvv_sincos)
                                              ^~~~~~~~~~~~~~~~~
../sysdeps/x86_64/fpu/test-double-vlen2-wrappers.c:33:46: error: 'mr' is used uninitialized in this function [-Werror=uninitialized]
../sysdeps/x86_64/fpu/test-double-vlen4-wrappers.c: In function 'sincos_vlen4':
../sysdeps/x86_64/fpu/test-double-vlen4-wrappers.c:34:46: error: 'mr1' is used uninitialized in this function [-Werror=uninitialized]
 VECTOR_WRAPPER_fFF_3 (WRAPPER_NAME (sincos), _ZGVcN4vvv_sincos)
                                              ^~~~~~~~~~~~~~~~~
../sysdeps/x86_64/fpu/test-double-vlen4-wrappers.c:34:46: error: 'mr' is used uninitialized in this function [-Werror=uninitialized]
gcc ../sysdeps/x86_64/fpu/test-double-vlen4-avx2-wrappers.c -c -std=gnu11 -fgnu89-inline  -O3 -Wall -Werror -Wundef -Wwrite-strings -fasynchronous-unwind-tables -fmerge-all-constants -fno-asynchronous-unwind-tables -frounding-math -fstack-protector-strong -g -mtune=generic -Wstrict-prototypes -Wold-style-definition   -mavx2       -D__NO_MATH_INLINES -D__LIBC_INTERNAL_MATH_INLINES -I../include -I/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math  -I/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux  -I../sysdeps/unix/sysv/linux/x86_64/64  -I../sysdeps/unix/sysv/linux/x86_64  -I../sysdeps/unix/sysv/linux/x86  -I../sysdeps/unix/sysv/linux/wordsize-64  -I../sysdeps/x86_64/nptl  -I../sysdeps/unix/sysv/linux/include -I../sysdeps/unix/sysv/linux  -I../sysdeps/nptl  -I../sysdeps/pthread  -I../sysdeps/gnu  -I../sysdeps/unix/inet  -I../sysdeps/unix/sysv  -I../sysdeps/unix/x86_64  -I../sysdeps/unix  -I../sysdeps/posix  -I../sysdeps/x86_64/64  -I../sysdeps/x86_64/fpu/multiarch  -I../sysdeps/x86_64/fpu  -I../sysdeps/x86/fpu/include -I../sysdeps/x86/fpu  -I../sysdeps/x86_64/multiarch  -I../sysdeps/x86_64  -I../sysdeps/x86  -I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96  -I../sysdeps/ieee754/dbl-64/wordsize-64  -I../sysdeps/ieee754/dbl-64  -I../sysdeps/ieee754/flt-32  -I../sysdeps/wordsize-64  -I../sysdeps/ieee754  -I../sysdeps/generic  -I.. -I../libio -I. -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -isystem /usr/include  -D_LIBC_REENTRANT -include /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/libc-modules.h -DMODULE_NAME=nonlib -include ../include/libc-symbols.h       -DTOP_NAMESPACE=glibc -o /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-wrappers.o -MD -MP -MF /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-wrappers.o.dt -MT /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-wrappers.o
gcc /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-exp.c -c -std=gnu11 -fgnu89-inline  -O3 -Wall -Werror -Wundef -Wwrite-strings -fasynchronous-unwind-tables -fmerge-all-constants -fno-asynchronous-unwind-tables -frounding-math -fstack-protector-strong -g -mtune=generic -Wstrict-prototypes -Wold-style-definition       -fno-builtin -D__FAST_MATH__ -DTEST_FAST_MATH -fno-inline -ffloat-store -D_OPENMP=201307 -Wno-unknown-pragmas    -D__NO_MATH_INLINES -D__LIBC_INTERNAL_MATH_INLINES -I../include -I/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math  -I/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux  -I../sysdeps/unix/sysv/linux/x86_64/64  -I../sysdeps/unix/sysv/linux/x86_64  -I../sysdeps/unix/sysv/linux/x86  -I../sysdeps/unix/sysv/linux/wordsize-64  -I../sysdeps/x86_64/nptl  -I../sysdeps/unix/sysv/linux/include -I../sysdeps/unix/sysv/linux  -I../sysdeps/nptl  -I../sysdeps/pthread  -I../sysdeps/gnu  -I../sysdeps/unix/inet  -I../sysdeps/unix/sysv  -I../sysdeps/unix/x86_64  -I../sysdeps/unix  -I../sysdeps/posix  -I../sysdeps/x86_64/64  -I../sysdeps/x86_64/fpu/multiarch  -I../sysdeps/x86_64/fpu  -I../sysdeps/x86/fpu/include -I../sysdeps/x86/fpu  -I../sysdeps/x86_64/multiarch  -I../sysdeps/x86_64  -I../sysdeps/x86  -I../sysdeps/ieee754/ldbl-96/include -I../sysdeps/ieee754/ldbl-96  -I../sysdeps/ieee754/dbl-64/wordsize-64  -I../sysdeps/ieee754/dbl-64  -I../sysdeps/ieee754/flt-32  -I../sysdeps/wordsize-64  -I../sysdeps/ieee754  -I../sysdeps/generic  -I.. -I../libio -I. -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/7/include -isystem /usr/include  -D_LIBC_REENTRANT -include /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/libc-modules.h -DMODULE_NAME=nonlib -include ../include/libc-symbols.h       -DTOP_NAMESPACE=glibc -o /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-exp.o -MD -MP -MF /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-exp.o.dt -MT /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-exp.o
cc1: all warnings being treated as errors
make[2]: *** [/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/sysd-rules:553: /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen2-wrappers.o] Error 1
make[2]: *** Waiting for unfinished jobs....
cc1: all warnings being treated as errors
make[2]: *** [/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/sysd-rules:553: /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-wrappers.o] Error 1
../sysdeps/x86_64/fpu/test-double-vlen4-avx2-wrappers.c: In function 'sincos_vlen4_avx2':
../sysdeps/x86_64/fpu/test-double-vlen4-avx2-wrappers.c:40:46: error: 'mr1' is used uninitialized in this function [-Werror=uninitialized]
 VECTOR_WRAPPER_fFF_2 (WRAPPER_NAME (sincos), _ZGVdN4vvv_sincos)
                                              ^~~~~~~~~~~~~~~~~
../sysdeps/x86_64/fpu/test-double-vlen4-avx2-wrappers.c:40:46: error: 'mr' is used uninitialized in this function [-Werror=uninitialized]
cc1: all warnings being treated as errors
make[2]: *** [/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/sysd-rules:553: /home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/build-x86_64-redhat-linux/math/test-double-vlen4-avx2-wrappers.o] Error 1
make[2]: Leaving directory '/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4/math'
make[1]: *** [Makefile:215: math/tests] Error 2
make[1]: Leaving directory '/home/tkloczko/rpmbuild/BUILD/glibc-2.25-80-ga10e9c4'
++ status=2
++ echo 2
make: *** [Makefile:9: check] Error 2
+ status=2
+ sleep 10
+ kill 1055
+ echo ===================FAILED TESTS=====================
===================FAILED TESTS=====================
+ '[' 2 -ne 0 ']'
+ grep 'Summary of test results:' check.log
/var/tmp/rpm-tmp.ww62ip: line 36:  1055 Terminated              tail -f check.log
+ echo 'FAIL: Some glibc tests failed to build.'
FAIL: Some glibc tests failed to build.
+ exit 1
error: Bad exit status from /var/tmp/rpm-tmp.ww62ip (%check)