tccpp: Implement __COUNTER__

tccpp: Implement __COUNTER__

This requires one more change in how macro arguments are expanded:
the standard requires that macro args are expanded before substituting
into the replacement list.  This implies expanding them only once
even when they occur multiple times in the list.  TCC expanded
them repeatedly in that case.  Without __COUNTER__ that's harmless.

So, simply always expand arguments (when used without # and ##) once
and store the resulting tokens.