Don't call realloc with size=0 to free data.

Newer versions of the C spec and POSIX have changed the behavior of
realloc called with size 0 to be implementation defined.

jsstate.c

@@ -10,15 +10,10 @@
 
 static void *js_defaultalloc(void *actx, void *ptr, int size)
 {
-#ifndef __has_feature
-#define __has_feature(x) 0
-#endif
-#if __has_feature(address_sanitizer) || defined(__SANITIZE_ADDRESS__)
 	if (size == 0) {
 		free(ptr);
 		return NULL;
 	}
-#endif
 	return realloc(ptr, (size_t)size);
 }