PR gdb/11557

	PR gdb/11557

	gdb/
	* regcache.c (registers_changed): Rename to ...
	(registers_changed_ptid): ... this, and only delete register cache
	entries matching the ptid filter argument.
	(registers_changed): Reimplement on top of registers_changed_ptid.
	* regcache.h (registers_changed_ptid): Declare.
	* target.c (target_resume): Flush register caches.

	gdb/testsuite/
	* gdb.mi/mi-ns-stale-regcache.exp, gdb.mi/ns-stale-regcache.c: New
	files.