bfd, opcodes, libctf: support --with-included-gettext

bfd, opcodes, libctf: support --with-included-gettext

Right now, these libraries hardwire -L../intl -lintl on a few fixed
platforms, which works fine on those platforms but on other platforms
leads to shared libraries that lack libintl_* symbols when configured
--with-included-gettext, and/or static libraries that contain libintl as
*another* static library.  If we instead use the LIBINTL variable
defined in ../intl/config.intl, this gives us the right thing on all
three classes of platform (gettext in libc, gettext in system libintl,
gettext in ../intl/libintl.a)..  This also means we can rip out some
Darwin-specific machinery from configure.ac and also simplify the Cygwin
side.

This also means that the libctf testsuite (and other places that include
libbfd, libopcodes or libctf) don't need to grow libintl dependencies
just on account of those libraries (though they still need such
dependencies if they themselves use gettext machinery).

bfd/ChangeLog
2021-02-03  Nick Alcock  <nick.alcock@oracle.com>

	* configure.ac (SHARED_LIBADD): Remove explicit -lintl population in
	favour of LIBINTL.
	* configure: Regenerated.

libctf/ChangeLog
2021-02-02  Nick Alcock  <nick.alcock@oracle.com>

	* configure.ac (CTF_LIBADD): Remove explicit -lintl population in
	favour of LIBINTL.
	* Makefile.am (libctf_nobfd_la_LIBADD): No longer explicitly
	include $(LIBINTL).
	(check-DEJAGNU): Pass down to tests as well.
	* configure: Regenerated.
	* Makefile.in: Likewise.

opcodes/ChangeLog
2021-02-04  Nick Alcock  <nick.alcock@oracle.com>

	* configure.ac (SHARED_LIBADD): Remove explicit -lintl population in
	favour of LIBINTL.
	* configure: Regenerated.