* configure.ac (MALLOC_OFILES): Add ptmalloc3.o.
	* configure: Regenerate.
	* cygmalloc.h: Declare pt* functions rather than dl* functions.
	(mmap64): Declare.
	(mmap): Define as mmap64.
	(__malloc_lock): Drop macro.
	(__malloc_unlock): Ditto.
	(MSPACES): Define.
	(ONLY_MSPACES): Define.
	* debug.h: Include malloc.h rather than otherwise unused dlmalloc.h.
	* fork.cc (frok::parent): Drop malloc locking since that's performed
	by malloc_atfork now.
	* heap.cc (heap_init): Accommodate the fact that there's a chance
	that no heap space has been allocated at fork time.
	* malloc-private.h: New file from ptmalloc3, having malloc-machine.h
	and malloc-2.8.3.h folded in.
	* malloc.cc: Replaced by new file from ptmalloc3.
	* malloc_wrapper.cc: Throughout, remove malloc locks and call pt*
	functions rather than dl* functions.
	* pinfo.cc (winpids::set): Drop malloc locking.
	* ptmalloc3.cc: New file from ptmalloc3.
	* include/cygwin/signal.h (struct ucontext): Add missing fields from
	Windows CONTEXT definition.  Define oldmask as 64 bit type.
Merge branch 'cygwin64' into msys2-64-dev