Fix gdbserver build when intl already built

Fix gdbserver build when intl already built

gdbserver uses gdb's alloc.c, and this in turn can include headers
from intl via gdbsupport/gdb_locale.h.  This can cause build failures
in some situations, for example if you build gdb and gdbserver on
mingw.

This patch restores the gdbsupport dependency on intl, and changes
gdbserver to use ZW_GNU_GETTEXT_SISTER_DIR.  This fixes this build
problem.

ChangeLog
2020-03-12  Tom Tromey  <tom@tromey.com>

	* Makefile.in: Rebuild.
	* Makefile.def (gdbsupport): Depend on intl.

gdbserver/ChangeLog
2020-03-12  Tom Tromey  <tom@tromey.com>

	* config.in, configure: Rebuild.
	* configure.ac: Call ZW_GNU_GETTEXT_SISTER_DIR.
	* acinclude.m4: Include gettext-sister.m4.
	* Makefile.in (top_builddir, INTL, INTL_DEPS, INTL_CFLAGS): New
	variables.
	(INCLUDE_CFLAGS): Add INTL_CFLAGS.
	(gdbserver$(EXEEXT), gdbreplay$(EXEEXT)): Use INTL_DEPS, INTL.