Add --with-system-zlib in gdb

Add --with-system-zlib in gdb

This patch adds --with-system-zlib and removes --with-zlib in gdb.

	* Makefile.in (ZLIB): New.
	(ZLIBINC): Likewise.
	(INTERNAL_CFLAGS_BASE): Add $(ZLIBINC).
	(CLIBS): Add $(ZLIB).
	* acinclude.m4: (GDB_AC_CHECK_BFD): Add $zlibdir to LDFLAGS.
	Add -lz to LIBS.
	* gdb_bfd.c: Don't check HAVE_ZLIB_H to include <zlib.h>.
	* top.c (print_gdb_configuration): Remove --with-zlib and
	--without-zlib.
	* config.in: Regenerated.
	* configure: Likewise.