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_mailslot.cc

@@ -146,7 +146,7 @@ fhandler_mailslot::open (int flags, mode_t mode)
   return res;
 }
 
-ssize_t __stdcall
+ssize_t __reg3
 fhandler_mailslot::raw_write (const void *ptr, size_t len)
 {
   /* Check for 425/426 byte weirdness */