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_tty.cc

@@ -684,7 +684,7 @@ fhandler_pty_slave::write (const void *ptr, size_t len)
   return towrite;
 }
 
-void __stdcall
+void __reg3
 fhandler_pty_slave::read (void *ptr, size_t& len)
 {
   ssize_t totalread = 0;
@@ -1150,7 +1150,7 @@ fhandler_pty_slave::fch_close_handles ()
   close_maybe (inuse);
 }
 
-int __stdcall
+int __reg1
 fhandler_pty_slave::fchmod (mode_t mode)
 {
   int ret = -1;
@@ -1176,7 +1176,7 @@ errout:
   return ret;
 }
 
-int __stdcall
+int __reg2
 fhandler_pty_slave::fchown (uid_t uid, gid_t gid)
 {
   int ret = -1;
@@ -1355,7 +1355,7 @@ fhandler_pty_master::write (const void *ptr, size_t len)
   return i;
 }
 
-void __stdcall
+void __reg3
 fhandler_pty_master::read (void *ptr, size_t& len)
 {
   bg_check_types bg = bg_check (SIGTTIN);