libctf: support platforms with separate libintl

libctf: support platforms with separate libintl

We were not using the right configure machinery to spot libintl on
platforms where it was required, leading to the spurious failure of
various configure tests (e.g. for things like ELF support in BFD).

libctf/
	* aclocal.m4: Add config/gettext-sister.m4: Shuffle into
	alphabetical order.
	* configure.ac: Add ZW_GNU_GETTEXT_SISTER_DIR.
	* config.h.in: Regenerated.
	* Makefile.in: Likewise.
	* configure: Likewise.