Hi Fabian,
I've been thinking about this a bit, and cleaner would be to include a .c file but in its proper directory (so it gets compiled by itself).
For example, say in user32 we have the large implementation (with #ifdefs) of combo.c, at the top it has something like:
#ifndef CONTROL_VERSION #define CONTROL_VERSION 1 #endif
And gets compiled as normal. Then in comctl32's combo.c we'd have something like:
#define CONTROL_VERSION 2 #include "../user32/combo.c"
Seems cleaner to me.