Change gdbserver to use existing gdbsupport

Change gdbserver to use existing gdbsupport

This changes the gdbserver build to use the gdbsupport that was built
for gdb.

gdbserver and gdbreplay now must use WIN32APILIBS (aka -lws2_32).
Before this change, gdbserver did not define USE_WIN32API when
building gdbsupport, but now this is always done.

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

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

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

	* configure: Rebuild.
	* configure.ac (GDBSERVER_DEPFILES): Remove srv_selftest_objs.
	(WIN32APILIBS): New subst.
	* Makefile.in (SFILES, OBS, TAGS, GDBREPLAY_OBS): Remove
	gdbsupport files.
	(gdbsupport/%.o): Remove target.
	(GDBSUPPORT_BUILDDIR, GDBSUPPORT): New variables.
	(gdbserver$(EXEEXT), gdbreplay$(EXEEXT)): Add GDBSUPPORT.
	(WIN32APILIBS): New variable.
	(gdbserver$(EXEEXT)): Add WIN32APILIBS.
	(gdbreplay$(EXEEXT)): Likewise.