cppinit.c (cpp_create_reader, [...]): Warn about trigraphs unless explicity set or...

cppinit.c (cpp_create_reader, [...]): Warn about trigraphs unless explicity set or -trigraphs.

	* cppinit.c (cpp_create_reader, post_options): Warn about
	trigraphs unless explicity set or -trigraphs.
	* cpplex.c (warn_in_comment): New.
	(_cpp_process_line_notes): Better handling of -Wtrigraphs.
	(_cpp_skip_block_comment): Add call to _cpp_process_line_notes.
	* doc/cppopts.texi, doc/cpp.texi: Update.
testsuite:
	* gcc.dg/cpp/Wtrigraphs.c: Update.
	* gcc.dg/cpp/Wtrigraphs-2.c: New tests.

From-SVN: r66459