pdp11 - example of a port not needing a speculation barrier

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