* c-common.c (warn_multichar): New.
	(c_common_init): Set CPP's warn_multichar.
	* c-common.h (warn_multichar): New.
	* c-decl.c (warn_multichar): Remove.
	* c-lex.c (lex_charconst): Update.
	* c-tree.h (warn_multichar): Remove.
	* cppexp.c (eval_token): Sign-extend charconst value.
	* cppinit.c (cpp_create_reader): Set warn_multichar.
	* cpplex.c (cpp_interpret_charconst): Don't sign-extend
	each character.  Update prototype.  Sign-extend the result.
	* cpplib.h: Fix conditions.
	(struct cpp_options): Add new warning flag.
	(cpp_interpret_charconst): Update prototype.
cp:
	* Make-lang.in (decl2.o): Update.
	* cp-tree.h (warn_multichar): Remove.
	* decl2.c: Include c-common.h.
	(warn_multichar): Remove.
doc:
	* cpp.texi: Update documentation.
testsuite:
	* gcc.dg/cpp/charconst-3.c: Correct tests accordingly.

From-SVN: r53240