* cppinit.c (cpp_handle_option): Recognize C++ comments under
	-std=gnu89.
	* cpplib.c (skip_block_comment, skip_line_comment): Split code
	out of...
	(skip_comment) ... here.  Permit C++ comments in system
	headers always.  Warn about C++ comments in user code under
	-std=gnu89 -pedantic.
	(copy_comment): Use skip_comment.
	(cpp_skip_hspace, cpp_get_token): skip_comment can no longer
	return EOF.
	(consider_directive_while_skipping, do_else, do_endif): Call
	validate_else unconditionally.
	(validate_else): Check CPP_PEDANTIC here.  Accept non-comment
	text after the conditional in a system header.
	* cpplib.h (struct cpp_buffer): Add flag
	warned_cplusplus_comments.

From-SVN: r31654