* c-common.c (STDC_0_IN_SYSTEM_HEADERS, REGISTER_PREFIX):
	Default-define here.
	(builtin_define_with_value): Can now wrap the expansion in
	quotation marks if such is wanted.
	(cb_register_builtins): Update calls to	builtin_define_with_value.
	Define __REGISTER_PREFIX__, __USER_LABEL_PREFIX__, and __VERSION__
	here.
	(c_common_init): Set options->stdc_0_in_system_headers.
	* c-lex.h: Update prototype of builtin_define_with_value.
	* cppdefault.h: Remove default definitions of USER_LABEL_PREFIX
	and REGISTER_PREFIX.

	* cppinit.c (VERS, ULP, C, X): Kill.
	(builtin_array): Remove entries for __VERSION__,
	__USER_LABEL_PREFIX__, __REGISTER_PREFIX__, and
	__HAVE_BUILTIN_SETJMP__.  Make __STDC__ always a builtin, not
	a constant.
	(init_builtins): Kill off a bunch of now-dead code.
	(COMMAND_LINE_OPTIONS): Remove -fleading-underscore and
	-fno-leading-underscore.
	(cpp_handle_option): Remove code to set user_label_prefix.
	(cpp_post_options): Likewise.

	* cpplib.h (struct cpp_options): Remove user_label_prefix.
	(stdc_0_in_system_headers): New.
	* cppmacro.c (builtin_macro): Check CPP_OPTION (pfile,
	stdc_0_in_system_headers) too to decide the value of __STDC__.

	* tradcpp.c (user_label_prefix): Kill.
	(main): Remove code handling -f(no-)leading-underscore.
	(initialize_builtins): Don't define __REGISTER_PREFIX__
	or __USER_LABEL_PREFIX__.
	(install_value): Wrap compound statement in dummy loop so the
	macro works properly in an if statement.

From-SVN: r53525