Fix sizeof(http_parser) assert

The result should be 32 on both 32 bits and 64 bits x86 because of
struct padding.

Fixes: nodejs#507
PR-URL: nodejs#510
Reviewed-By: Fedor Indutny <fedor.indutny@gmail.com>

test.c

@@ -4343,7 +4343,13 @@ main (void)
   printf("http_parser v%u.%u.%u (0x%06lx)\n", major, minor, patch, version);
 
   printf("sizeof(http_parser) = %u\n", (unsigned int)sizeof(http_parser));
-  assert(sizeof(http_parser) == 4 + 4 + 8 + 2 + 2 + 4 + sizeof(void *));
+
+#if defined(__i386__) || defined(__x86_64__)
+  /* Should be 32 on both 32 bits and 64 bits x86 because of struct padding,
+   * see https://github.com/nodejs/http-parser/issues/507.
+   */
+  assert(sizeof(http_parser) == 32);
+#endif
 
   //// API
   test_preserve_data();