* 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
