gdbserver: Use pattern rule for objects from common/

gdbserver: Use pattern rule for objects from common/

gdb/gdbserver/ChangeLog:

	* Makefile.in (%.o: ../common/%.c): New rule.
	(signals.o: ../common/signals.c): Remove.
	(print-utils.o: ../common/print-utils.c): Remove.
	(rsp-low.o: ../common/rsp-low.c): Remove.
	(common-utils.o: ../common/common-utils.c): Remove.
	(posix-strerror.o: ../common/posix-strerror.c): Remove.
	(mingw-strerror.o: ../common/mingw-strerror.c): Remove.
	(vec.o: ../common/vec.c): Remove.
	(gdb_vecs.o: ../common/gdb_vecs.c): Remove.
	(xml-utils.o: ../common/xml-utils.c): Remove.
	(ptid.o: ../common/ptid.c): Remove.
	(buffer.o: ../common/buffer.c): Remove.
	(format.o: ../common/format.c): Remove.
	(filestuff.o: ../common/filestuff.c): Remove.
	(agent.o: ../common/agent.c): Remove.
	(errors.o: ../common/errors.c): Remove.
	(environ.o: ../common/environ.c): Remove.
	(common-debug.o: ../common/common-debug.c): Remove.
	(cleanups.o: ../common/cleanups.c): Remove.
	(common-exceptions.o: ../common/common-exceptions.c): Remove.
	(fileio.o: ../common/fileio.c): Remove.
	(common-regcache.o: ../common/common-regcache.c): Remove.
	(signals-state-save-restore.o: ../common/signals-state-save-restore.c): Remove.
	(new-op.o: ../common/new-op.c): Remove.
	(btrace-common.o: ../common/btrace-common.c): Remove.