* wincap.h (wincaps::has_always_all_codepages): New element.

* wincap.cc: Implement above element throughout.
	* wchar.h (__sjis_mbtowc): Declare.
	(__eucjp_mbtowc): Ditto.
	(__gbk_mbtowc): Ditto.
	(__kr_mbtowc): Ditto.
	(__big5_mbtowc): Ditto.
	* syscalls.cc (internal_setlocale): Convert to char * function.
	Return parameter by default.  Return NULL if request to use a
	charset can't be satisfied due to missing codepage support in the
	underlying OS.  Fix comment.
	(setlocale): Store original locale.  Restore to original locale if
	internal_setlocale returns NULL.

winsup/cygwin/wincap.h

@@ -48,6 +48,7 @@ struct wincaps
   unsigned has_broken_udf				: 1;
   unsigned has_console_handle_problem			: 1;
   unsigned has_broken_alloc_console			: 1;
+  unsigned has_always_all_codepages			: 1;
 };
 
 class wincapc
@@ -102,6 +103,7 @@ public:
   bool	IMPLEMENT (has_broken_udf)
   bool	IMPLEMENT (has_console_handle_problem)
   bool	IMPLEMENT (has_broken_alloc_console)
+  bool	IMPLEMENT (has_always_all_codepages)
 
 #undef IMPLEMENT
 };