libxslt-devel-1.1.29-1.fc27 has /usr/include/libxslt/xsltlocale.h that includes <xlocale.h> that was removed from glibc-2.25.90-8. The removal is intentional.

This breaks building any packages that include <libxslt/xsltlocale.h>. E.g. perl-XML-LibXSLT:

gcc -c  -I/usr/include/libxml2 -I/usr/include/libxml2  -D_REENTRANT -D_GNU_SOURCE -O2 -g -pipe -Wall -Werror=format-security -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 -fwrapv -fno-strict-aliasing -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -O2 -g -pipe -Wall -Werror=format-security -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   -DVERSION=\"1.95\" -DXS_VERSION=\"1.95\" -fPIC "-I/usr/lib64/perl5/CORE"  -DHAVE_BLANK -DHAVE_BLANK -DHAVE_EXSLT LibXSLT.c
In file included from /usr/include/libxslt/xsltInternals.h:24:0,
                 from LibXSLT.xs:14:
/usr/include/libxslt/xsltlocale.h:20:10: fatal error: xlocale.h: No such file or directory
 #include <xlocale.h>
          ^~~~~~~~~~~

Please rebuild libxslt to stop including the header file.