cmocka: fix setjmp in expect_assert_failure macro

Assigning the result of `setjmp` to a variable is technically
undefined behavior in the C standard.

Most platforms allow this (NetBSD even uses this syntax in their tests)
and GCC/Clang doesn't even give us a warning. Nonetheless, we should
follow the ISO C specification.

See [§ 7.13.1.1.4 of the C99 spec.][1]

[1]: https://www.open-std.org/JTC1/SC22/WG14/www/docs/n1256.pdf
on-behalf-of: @nqminds <info@nqminds.com>

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

include/cmocka.h

@@ -2314,9 +2314,8 @@ void expect_assert_failure(function fn_call);
 #else
 #define expect_assert_failure(function_call) \
   { \
-    const int result = setjmp(global_expect_assert_env); \
     global_expecting_assert = 1; \
-    if (result) { \
+    if (setjmp(global_expect_assert_env) != 0) { \
       print_message("Expected assertion %s occurred\n", \
                     global_last_failed_assert); \
       global_expecting_assert = 0; \