pdp11 - example of a port not needing a speculation barrier

This patch is intended as an example of all that is needed if the
target system doesn't support CPUs that have speculative execution.
I've chosen the pdp11 port on the basis that it's old enough that this
is likely to be true for all existing implementations and that there
is also little chance of that changing in future!

	* config/pdp11/pdp11.c (TARGET_HAVE_SPECULATION_SAFE_VALUE): Redefine
	to speculation_safe_value_not_needed.

From-SVN: r263176

gcc/ChangeLog

 2018-07-31  Richard Earnshaw  <rearnsha@arm.com>
 
+	* config/pdp11/pdp11.c (TARGET_HAVE_SPECULATION_SAFE_VALUE): Redefine
+	to speculation_safe_value_not_needed.
+
+2018-07-31  Richard Earnshaw  <rearnsha@arm.com>
+
 	* 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.

gcc/config/pdp11/pdp11.c

@@ -291,6 +291,9 @@ static bool pdp11_scalar_mode_supported_p (scalar_mode);
 
 #undef TARGET_INVALID_WITHIN_DOLOOP
 #define TARGET_INVALID_WITHIN_DOLOOP hook_constcharptr_const_rtx_insn_null
+
+#undef TARGET_HAVE_SPECULATION_SAFE_VALUE
+#define TARGET_HAVE_SPECULATION_SAFE_VALUE speculation_safe_value_not_needed
 
 /* A helper function to determine if REGNO should be saved in the
    current function's stack frame.  */