errno.h is included in common/common-defs.h, and gnulib errno module
was imported to gdb. This patch is to import it explicitly.
gdb:
* gnulib/update-gnulib.sh (IMPORTED_GNULIB_MODULES): Add
errno.
* gnulib/import/Makefile.am: Re-generated.
* gnulib/import/Makefile.in: Likewise.
* gnulib/import/m4/gnulib-cache.m4: Likewise.