* doc/cppopts.texi: Clarify processing of command-line defines.

libcpp:
	PR preprocessor/16192
	PR preprocessor/15913
	PR preprocessor/15572
	* expr.c (_cpp_parse_expr): Handle remaining cases where an
	expression is missing.
	* init.c (post_options): Traditional cpp doesn't do // comments.

testsuite:
	* gcc.dg/cpp/if-mop.c: Two new testcases.
	* gcc.dg/cpp/trad/comment-3.c: New.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@84080 138bc75d-0d04-0410-961f-82ee72b054a4