Makefile.include: Only evaluate RIOT_VERSION when needed
Makefile.include: Only evaluate RIOT_VERSION when needed

This changes CFLAGS_WITH_MACROS to be:

* a deferred variable
* not exported so only evaluated when actually used

The value is only used by `Makefile.include` and `makefiles/eclipse.inc.mk`
so not required to export it.

rfuentess/RIOT,mtausig/RIOT,OlegHahm/RIOT,kYc0o/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,mtausig/RIOT,miri64/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,basilfx/RIOT,kYc0o/RIOT,kYc0o/RIOT,kYc0o/RIOT,ant9000/RIOT,josephnoir/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,mtausig/RIOT,yogo1212/RIOT,ant9000/RIOT,toonst/RIOT,authmillenon/RIOT,aeneby/RIOT,x3ro/RIOT,OTAkeys/RIOT,aeneby/RIOT,OTAkeys/RIOT,RIOT-OS/RIOT,aeneby/RIOT,OTAkeys/RIOT,jasonatran/RIOT,rfuentess/RIOT,authmillenon/RIOT,josephnoir/RIOT,cladmi/RIOT,toonst/RIOT,smlng/RIOT,yogo1212/RIOT,miri64/RIOT,kaspar030/RIOT,yogo1212/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,OlegHahm/RIOT,rfuentess/RIOT,ant9000/RIOT,basilfx/RIOT,kaspar030/RIOT,toonst/RIOT,rfuentess/RIOT,miri64/RIOT,rfuentess/RIOT,x3ro/RIOT,x3ro/RIOT,aeneby/RIOT,kaspar030/RIOT,mtausig/RIOT,miri64/RIOT,cladmi/RIOT,josephnoir/RIOT,jasonatran/RIOT,yogo1212/RIOT,jasonatran/RIOT,ant9000/RIOT,cladmi/RIOT,cladmi/RIOT,kaspar030/RIOT,smlng/RIOT,OlegHahm/RIOT,smlng/RIOT,kYc0o/RIOT,miri64/RIOT,basilfx/RIOT,smlng/RIOT,authmillenon/RIOT,authmillenon/RIOT,basilfx/RIOT,toonst/RIOT,mtausig/RIOT,aeneby/RIOT,cladmi/RIOT,yogo1212/RIOT,smlng/RIOT,ant9000/RIOT,OTAkeys/RIOT,jasonatran/RIOT,x3ro/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,jasonatran/RIOT,basilfx/RIOT,x3ro/RIOT,OTAkeys/RIOT,authmillenon/RIOT,toonst/RIOT