compiler.h: only use __no_stack_protector if supported by the compiler

The __attribute__((no_stack_protector)) was introduced in GCC 11.
Building a TA with a version of GCC older than that would trigger a
-Wattributes warning on the ta/user_ta_header.c file.

Use __has_attribute() to check support of the no_stack_protector
attribute before using it. If not supported, define the
__no_stack_protector alias as a NOP.

Fixes: e3fb2bd ("compiler.h: add __no_stack_protector")
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>

lib/libutils/ext/include/compiler.h

@@ -15,6 +15,11 @@
  * the conflicting defines has the same meaning in that environment.
  * Surrounding the troublesome defines with #ifndef should be enough.
  */
+
+#ifndef __has_attribute
+#define __has_attribute(x) 0
+#endif
+
 #define __deprecated	__attribute__((deprecated))
 #ifndef __packed
 #define __packed	__attribute__((packed))
@@ -24,9 +29,15 @@
 #ifndef __noreturn
 #define __noreturn	__attribute__((__noreturn__))
 #endif
+
 #ifndef __no_stack_protector
+#if __has_attribute(no_stack_protector)
 #define __no_stack_protector __attribute__((no_stack_protector))
+#else
+#define __no_stack_protector
 #endif
+#endif
+
 #define __pure		__attribute__((pure))
 #define __aligned(x)	__attribute__((aligned(x)))
 #define __printf(a, b)	__attribute__((format(printf, a, b)))