Adjust to latest gnulib.

(gnulib_modules): Add xalloc-die.
Set LC_ALL=C so that file names sort consistently.
Prefer the gnulib copies of gettext.m4, glibc21.m4,
inttypes_h.m4, lib-ld.m4, lib-prefix.m4, po.m4, stdint_h.m4,
uintmax_t.m4, ulonglong.m4.
(intl_files_to_remove): Add gettext.m4, lib-ld.m4, lib-prefix.m4,
po.m4 since we are now using _gl.m4 instead.