Description of problem:
libreport fails to build from source in Rawhide with the get_ns_ids tests failing with an obscure error on aarch64, armv7hl, i686 and x86_64.
The build & tests pass just fine on ppc64, ppc64le and s390x.

Perhaps it's related to optflags or builder configuration?

Build log snippet (same for all affected arches):

110: get_ns_ids                                      FAILED (proc_helpers.at:708)
111: get_mountinfo_for_mount_point                   ok
112: dump_namespace_diff                             ok
113: process_has_own_root                            ok
compress
114: lz4-decompression                               ok
115: xz-decompression                                ok
Forbidden words
116: load_words_from_file                            ok
Client
117: set_echo                                        ok
## ------------- ##
## Test results. ##
## ------------- ##
ERROR: All 117 tests were run,
1 failed unexpectedly.
## -------------------------- ##
## testsuite.log was created. ##
## -------------------------- ##
Please send `tests/testsuite.log' and all information you think might help:
   To: <crash-catcher>
   Subject: [libreport 2.9.2] testsuite: 110 failed
You may investigate any problem if you feel able to do so, in which
case the test suite provides a good starting point.  Its output may
be found below `tests/testsuite.dir'.
make[2]: *** [Makefile:749: check-local] Error 1
make[2]: Leaving directory '/builddir/build/BUILD/libreport-2.9.2/tests'
make[1]: Leaving directory '/builddir/build/BUILD/libreport-2.9.2/tests'
make[1]: *** [Makefile:603: check-am] Error 2
make: *** [Makefile:633: check-recursive] Error 1
+ find tests/testsuite.dir -name testsuite.log -print -exec cat '{}' ';'
tests/testsuite.dir/110/testsuite.log
#                             -*- compilation -*-
110. proc_helpers.at:708: testing get_ns_ids ...
./proc_helpers.at:708: $LIBTOOL --mode=link $CC $CFLAGS $LDFLAGS -o get_ns_ids get_ns_ids.c $LIBS
stderr:
In file included from /usr/include/assert.h:35:0,
                 from /builddir/build/BUILD/libreport-2.9.2/src/include/internal_libreport.h:23,
                 from /builddir/build/BUILD/libreport-2.9.2/tests/helpers/testsuite.h:88,
                 from proc_helpers.at:709:
/usr/include/features.h:376:4: warning: #warning _FORTIFY_SOURCE requires compiling with optimization (-O) [-Wcpp]
 #  warning _FORTIFY_SOURCE requires compiling with optimization (-O)
    ^~~~~~~
stdout:
libtool: link: gcc -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -m64 -mtune=generic -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -fno-strict-aliasing -std=gnu99 -Wall -Wwrite-strings -I/builddir/build/BUILD/libreport-2.9.2/tests/helpers -I/builddir/build/BUILD/libreport-2.9.2/src/include -I/builddir/build/BUILD/libreport-2.9.2/src/lib -I/builddir/build/BUILD/libreport-2.9.2/src/gtk-helpers -D_GNU_SOURCE -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/gtk-3.0 -I/usr/include/pango-1.0 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/harfbuzz -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/gio-unix-2.0/ -I/usr/include/atk-1.0 -I/usr/include/at-spi2-atk/2.0 -I/usr/include/at-spi-2.0 -I/usr/include/dbus-1.0 -I/usr/lib64/dbus-1.0/include -pthread -DDEFAULT_DUMP_DIR_MODE=0x1A0 -Wl,-z -Wl,relro -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -o .libs/get_ns_ids get_ns_ids.c  /builddir/build/BUILD/libreport-2.9.2/src/gtk-helpers/.libs/libreport-gtk.so -lgtk-3 -lgdk-3 -lpangocairo-1.0 -lpango-1.0 -latk-1.0 -lcairo-gobject -lcairo -lgdk_pixbuf-2.0 -lgio-2.0 /builddir/build/BUILD/libreport-2.9.2/src/lib/.libs/libreport-web.so -lcurl -lproxy -lxml2 -ljson-c -lxmlrpc -lxmlrpc_util -lxmlrpc_client /builddir/build/BUILD/libreport-2.9.2/src/lib/.libs/libreport.so -ltar -lsystemd -lgobject-2.0 -lglib-2.0 -laugeas -lsatyr -lutil -pthread
./proc_helpers.at:708: $PRE_AT_CHECK ./get_ns_ids
stderr:
get_ns_ids
[ FAILED ] 742: pid_for_children (i < ARRAY_SIZE(libreport_proc_namespaces))
	Actual  : 7
	Expected: 7
get_ns_ids_at
[ FAILED ] 742: pid_for_children (i < ARRAY_SIZE(libreport_proc_namespaces))
	Actual  : 7
	Expected: 7
stdout:
./proc_helpers.at:708: exit code was 2, expected 0
110. proc_helpers.at:708: 110. get_ns_ids (proc_helpers.at:708): FAILED (proc_helpers.at:708)
+ exit 1
error: Bad exit status from /var/tmp/rpm-tmp.BSlmak (%check)


Version-Release number of selected component (if applicable):
libreport-2.9.2-1

How reproducible:
Always since roughly a week or less ago.
Building the same NVR on August 31 went okay.
Building it today fails every time with the same error on the same arches.

Steps to Reproduce:
1. [scratch] build 2.9.2-1 in Rawhide
2. Watch it fail with the abovementioned errors.

Actual results:
Test failures, FTBFS

Expected results:
The build & tests pass just like they did before.

Additional info:
FTR, buildroot differences between my modular passing and failing builds:
p11-kit: 0.23.8-1.fc27 -> 0.23.8-2.fc28
p11-kit-trust: 0.23.8-1.fc27 -> 0.23.8-2.fc28