defaults.h: Define PREFERRED_STACK_BOUNDARY to STACK_BOUNDARY if not already defined.

defaults.h: Define PREFERRED_STACK_BOUNDARY to STACK_BOUNDARY if not already defined.

	* defaults.h: Define PREFERRED_STACK_BOUNDARY to
	STACK_BOUNDARY if not already defined.

	* calls.c, function.c, reload1.c, explow.c: Don't default
	PREFERRED_STACK_BOUNDARY.  Remove all #if/#ifdef on
	PREFERRRED_STACK_BOUNDARY and/or STACK_BOUNDARY.

	* explow.c (allocate_dynamic_stack_space): Change unsafe #if
	to run-time test.

	* doc/tm.texi: Document that STACK_BOUNDARY is required;
	clarify difference between it and PREFERRED_STACK_BOUNDARY.

From-SVN: r44814