gOlogy: do not change code in isolate-paths for warnings only

gOlogy: do not change code in isolate-paths for warnings only

The isolate-paths pass is activated by various -f flags, but also by
-Wnull-dereference.  Most of its codegen changes are conditioned on at
least one of the -f flags, but those that detect, warn about and
isolate paths that return the address of local variables are enabled
even if the pass is activated only by -Wnull-dereference.

-W flags should not cause codegen changes, so this patch makes the
codegen changes conditional on the presence of any of the -f flags
that activate the pass.  Should we have a separate option to activate
only this kind of transformation?

for  gcc/ChangeLog

	* gimple-ssa-isolate-paths.c
	(find_implicit_erroneous_behavior): Do not change code if the
	pass is running for warnings only.
	(find_explicit_erroneous_behavior): Likewise.

From-SVN: r265473