testsuite - improve check_effective_target_cet.

In some cases the test using setssbsy was not enough to
detemine support for the CET insns.  Adding -fcf-protection
explicitly causes other insns to be emitted (e.g. endbr32/64)
which are a more complete check.

2019-05-16  Iain Sandoe  <iain@sandoe.co.uk>

	* lib/target-supports.exp (check_effective_target_cet): Add the
	-fcf-protection flag to the build conditions.

From-SVN: r271282

gcc/testsuite/ChangeLog

+2019-05-16  Iain Sandoe  <iain@sandoe.co.uk>
+
+	* lib/target-supports.exp (check_effective_target_cet): Add the
+	-fcf-protection flag to the build conditions.
+
 2019-05-16  Jun Ma <JunMa@linux.alibaba.com>
 
 	PR tree-optimization/90106

gcc/testsuite/lib/target-supports.exp

@@ -9225,7 +9225,7 @@ proc check_effective_target_cet { } {
 	{
 	  asm ("setssbsy");
 	}
-    } "-O2" ]
+    } "-O2 -fcf-protection" ]
 }
 
 # Return 1 if target supports floating point "infinite"