cpplex.c (parse_identifier): Fast-path optimize.

	* cpplex.c (parse_identifier): Fast-path optimize.  Avoid
	copying identifier when we're just going to throw it away.
	(parse_identifier_slow): New routine to handle abnormal cases.
	(_cpp_lex_token): Update call site.

	* hashtable.c (ht_lookup): Don't assume that the string we've
	been given is NUL-terminated.
	* system.h: #define __builtin_expect(a, b) to (a) if not
	GCC >=3.0.

From-SVN: r45529