* Makefile.in (DLL_OFILES): Add wow64.o.

	* Makefile.in (DLL_OFILES): Add wow64.o.
	* dcrt0.cc (CYGWIN_GUARD): Drop execute permission for stack, it's
	not used for stacks by the OS either.
	(child_info_fork::alloc_stack_hard_way): Ditto.
	(child_info_fork::alloc_stack): Don't alloc_stack_hard_way under WOW64
	if forked from a 64 bit parent.  Set child's StackBase to parent's
	StackBase.  Add comments to explain why.
	(wow64_respawn): Move to wow64.cc.
	(wow64_started_from_native64): Move to wow64.cc.
	(respawn_wow64_process): Move to wow64.cc.
	(dll_crt0_0): Drop wow64_test_stack_marker and move stack test into
	wow64_test_for_64bit_parent function.  Don't return early if WOW64
	process has been started from native 64 bit process.
	(_dll_crt0): Implement moving stack for WOW64 processes started from
	native 64 bit process.
	* wow64.cc: New file.
	(wow64_has_64bit_parent): Rename from wow64_respawn.
	(wow64_test_for_64bit_parent): Rename from wow64_started_from_native64.
	Change comment.
	(wow64_revert_to_original_stack): New function.
	(wow64_respawn_process): Rename from respawn_wow64_process for symmetry.
	* wow64.h: New file.