strerror-override: avoid bloating errno module * modules/errno (Files, configure.ac): Move replacement strings... * modules/strerror-override: ...to new module. * modules/strerror (Depends-on): Add strerror-override. * modules/strerror_r-posix (Depends-on): Likewise. * MODULES.html.sh: Document new module. Reported by Bruno Haible. Signed-off-by: Eric Blake <eblake@redhat.com>