LibC: Define static_assert in assert.h when it's being used in C

Author: https://github.com/RealKC
Commit: 35829304d6
Pull-request: https://github.com/SerenityOS/serenity/pull/5680

Userland/Libraries/LibC/assert.h

@@ -52,4 +52,8 @@ __attribute__((noreturn)) void __assertion_failed(const char* msg);
 #define VERIFY assert
 #define TODO VERIFY_NOT_REACHED
 
+#ifndef __cplusplus
+#    define static_assert _Static_assert
+#endif
+
 __END_DECLS