Throughout, (mainly in fhandler*) fix remaining gcc 4.7 mismatch

warnings between regparm definitions and declarations.
* smallprint.cc (__small_vswprintf): Conditionalize declaration and
setting of l_opt for only x86_64.
* spawn.cc (child_info_spawn::worker): Remove unused 'pid' variable.
* thread.cc (verifyable_object_isvalid): Temporarily define as
non-inline with gcc 4.7+, regardless of target.

winsup/cygwin/fhandler_zero.cc

@@ -41,7 +41,7 @@ fhandler_dev_zero::write (const void *, size_t len)
   return len;
 }
 
-void __stdcall
+void __reg3
 fhandler_dev_zero::read (void *ptr, size_t& len)
 {
   memset (ptr, 0, len);