[patch core/stackprotector] stackprotector: Fix build when compilerlacks support

[David Rientjes]

8779657d29c0 ("stackprotector: Introduce CONFIG_CC_STACKPROTECTOR_STRONG") 
causes the build to break when the compiler doesn't support 
-fstack-protector-strong:

	cc1: error: unrecognized command line option â-fstack-protector-strongâ
	cc1: error: unrecognized command line option â-fstack-protector-strongâ

with at least gcc 4.6.3.

Instead of breaking the build, just warn of the failure and disable the 
feature.

Signed-off-by: David Rientjes <rientjes@xxxxxxxxxx>
---
 Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -603,10 +603,11 @@ ifdef CONFIG_CC_STACKPROTECTOR_REGULAR
 	      -fstack-protector not supported by compiler))
   endif
 else ifdef CONFIG_CC_STACKPROTECTOR_STRONG
-  stackp-flag := -fstack-protector-strong
-  ifeq ($(call cc-option, $(stackp-flag)),)
+  ifeq ($(call cc-option, -fstack-protector-strong),)
     $(warning Cannot use CONFIG_CC_STACKPROTECTOR_STRONG: \
 	      -fstack-protector-strong not supported by compiler)
+  else
+    stackp-flag := -fstack-protector-strong
   endif
 else
   # Force off for distro compilers that enable stack protector by default.