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_tape.cc

@@ -1237,7 +1237,7 @@ fhandler_dev_tape::close ()
   return ret ? -1 : cret;
 }
 
-void __stdcall
+void __reg3
 fhandler_dev_tape::raw_read (void *ptr, size_t &ulen)
 {
   char *buf = (char *) ptr;
@@ -1339,7 +1339,7 @@ fhandler_dev_tape::raw_read (void *ptr, size_t &ulen)
   unlock ();
 }
 
-ssize_t __stdcall
+ssize_t __reg3
 fhandler_dev_tape::raw_write (const void *ptr, size_t len)
 {
   if (!_lock (true))