targhooks - provide an alternative hook for targets that never execute speculatively

targhooks - provide an alternative hook for targets that never execute speculatively

This hook adds an alternative implementation for the target hook
TARGET_HAVE_SPECULATION_SAFE_VALUE; it can be used by targets that have no
CPU implementations that execute code speculatively.  All that is needed for
such targets now is to add:

 #undef TARGET_HAVE_SPECULATION_SAFE_VALUE
 #define TARGET_HAVE_SPECULATION_SAFE_VALUE speculation_safe_value_not_needed.

to where you have your other target hooks and you're done.

gcc:
	* targhooks.h (speculation_safe_value_not_needed): New prototype.
	* targhooks.c (speculation_safe_value_not_needed): New function.
	* target.def (have_speculation_safe_value): Update documentation.
	* doc/tm.texi: Regenerated.

(backported 3e3448a9ae57194db317a72e68a3266a4cbdb39d)

Change-Id: I4532e9bc21029d5e452868dbe95c25a41d1f4a5c
git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@263175 138bc75d-0d04-0410-961f-82ee72b054a4