* c-common.h (flag_digraphs): New.
	* c-decl.c (c_decode_option): Set flag_digraphs as appropriate.
	* c-lex.c (yylex): Use flag_digraphs to decide whether to
	honour digraphs.

	* testsuite/gcc.dg/cpp/digraph1.c,
	testsuite/gcc.dg/cpp/digraph2.c,
	testsuite/gcc.dg/cpp/digraphs.c: New tests.

From-SVN: r35010