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_serial.cc

@@ -41,7 +41,7 @@ fhandler_serial::overlapped_setup ()
   overlapped_armed = 0;
 }
 
-void __stdcall
+void __reg3
 fhandler_serial::raw_read (void *ptr, size_t& ulen)
 {
   int tot;
@@ -167,7 +167,7 @@ out:
 
 /* Cover function to WriteFile to provide Posix interface and semantics
    (as much as possible).  */
-ssize_t __stdcall
+ssize_t __reg3
 fhandler_serial::raw_write (const void *ptr, size_t len)
 {
   DWORD bytes_written;