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_mem.cc

@@ -160,7 +160,7 @@ fhandler_dev_mem::write (const void *ptr, size_t ulen)
   return ulen;
 }
 
-void __stdcall
+void __reg3
 fhandler_dev_mem::read (void *ptr, size_t& ulen)
 {
   if (!ulen || pos >= (off_t) mem_size)