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/signal.cc

@@ -187,7 +187,7 @@ sigprocmask (int how, const sigset_t *set, sigset_t *oldset)
   return res;
 }
 
-int __stdcall
+int __reg3
 handle_sigprocmask (int how, const sigset_t *set, sigset_t *oldset, sigset_t& opmask)
 {
   /* check that how is in right range */
@@ -227,7 +227,7 @@ handle_sigprocmask (int how, const sigset_t *set, sigset_t *oldset, sigset_t& op
   return 0;
 }
 
-int __stdcall
+int __reg2
 _pinfo::kill (siginfo_t& si)
 {
   int res;