memchr has been used in gdb source and gnulib memchr module was
imported as a dependency. This patch is to import it explicitly.
gdb:
* gnulib/update-gnulib.sh (IMPORTED_GNULIB_MODULES): Add
memchr.
* gnulib/import/Makefile.am: Re-generated.
* gnulib/import/Makefile.in: Likewise.
* gnulib/import/m4/gnulib-cache.m4: Likewise.