opts.c (decode_options): Do language-specific initialization for the global diagnostic context.

	* opts.c (decode_options): Do language-specific initialization for
	the global diagnostic context.
	* langhooks-def.h (lhd_initialize_diagnostics): Declare.
	(LANG_HOOKS_INITIALIZE_DIAGNOSTITCS): New macro.
	(LANG_HOOKS_INITIALIZER): Adjust.
	* langhooks.h (struct lang_hooks): Add new field
	initialize_diagnostics.
	* langhooks.c (lhd_initialize_diagnostics): Define.

From-SVN: r70129