Don't shortcut macro expansion of non-parameter macros. It won't work once we have more kinds of expansion items than strings and arguments, viz., magic tokens for __FILE__ and __LINE__ and so on. (separate version of this applied against Joerg's changes, because we need to revert some of them)

/* make sure that R gets defined and doesn't end up part of a string */
#define Q "
#define R r
#define S "
R
Q