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_virtual.cc

@@ -181,7 +181,7 @@ fhandler_virtual::close ()
   return 0;
 }
 
-void __stdcall
+void __reg3
 fhandler_virtual::read (void *ptr, size_t& len)
 {
   if (len == 0)
@@ -266,7 +266,7 @@ fhandler_virtual::facl (int cmd, int nentries, aclent_t *aclbufp)
   return res;
 }
 
-int __stdcall
+int __reg2
 fhandler_virtual::fstatvfs (struct statvfs *sfs)
 {
   /* Virtual file system.  Just return an empty buffer with a few values