Disable stack protection explicitly

Explicitly disable stack protection via the "-fno-stack-protector"
compiler option when the ENABLE_STACK_PROTECTOR build option is
set to "none" (the default).

This allows the build to complete without link errors on systems where
stack protection is enabled by default in the compiler.

Change-Id: I0a676aa672815235894fb2cd05fa2b196fabb972
Signed-off-by: Simon South <simon@simonsouth.net>

lib/stack_protector/stack_protector.mk

@@ -11,7 +11,9 @@ ifeq (${ENABLE_STACK_PROTECTOR},0)
   ENABLE_STACK_PROTECTOR := none
 endif
 
-ifneq (${ENABLE_STACK_PROTECTOR},none)
+ifeq (${ENABLE_STACK_PROTECTOR},none)
+  TF_CFLAGS            +=      -fno-stack-protector
+else
   STACK_PROTECTOR_ENABLED := 1
   BL_COMMON_SOURCES	+=	lib/stack_protector/stack_protector.c	\
 				lib/stack_protector/${ARCH}/asm_stack_protector.S