Cosmetics: Add missing backslashes inside #defines

In all other multi-line comments inside #define there's a backslash at the end of the line just in case compiler strips comments after running preprocessor, and also to shut up some code highlighting editors (that's how I discovered this bug in the first place: #define took precedence over multi-line comment and lack of backshlash caused incorrect code highlighting). Now it's more consistent with the rest of the code. Quick grep didn't find any other affected files.