os_test: call_longjmp(): add __noreturn attribute

call_longjmp() does not return so it should have a __noreturn attribute.
Fixes a Clang warning:

 $ make COMPILER=clang
 ...
   CC      out/os_test.o
 os_test.c:667:1: warning: function 'call_longjmp' could be declared with attribute 'noreturn' [-Wmissing-noreturn]
 {
 ^

Signed-off-by: Jerome Forissier <jerome@forissier.org>
Reviewed-by: Etienne Carriere <etienne.carriere@linaro.org>
diff --git a/ta/os_test/os_test.c b/ta/os_test/os_test.c
index 7cc7088..a2c745b 100644
--- a/ta/os_test/os_test.c
+++ b/ta/os_test/os_test.c
@@ -663,7 +663,7 @@
 }
 #endif /*CFG_TA_FLOAT_SUPPORT*/
 
-static __noinline void call_longjmp(jmp_buf env)
+static __noinline __noreturn void call_longjmp(jmp_buf env)
 {
 	DMSG("Calling longjmp");
 	longjmp(env, 1);