2.8.0

Update to glibc 2.28

• regcomp.c: Update to glibc 2.28.
• regex.c: Likewise.
• regex.h: Likewise.
• regex_internal.c: Likewise.
• regex_internal.h: Likewise.
• regexec.c: Likewise.
• configure.ac: Bump to 2.8.0.
• configure: Regenerated.