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/pipe.cc

@@ -394,7 +394,7 @@ fhandler_pipe::ioctl (unsigned int cmd, void *p)
   return 0;
 }
 
-int __stdcall
+int __reg2
 fhandler_pipe::fstatvfs (struct statvfs *sfs)
 {
   set_errno (EBADF);