Friend wanted to know how to do this, just in case someone else does too here it is:
in the menu Build -> Set Includes and Arguments, add this to the end of the BUILD field:
Code:
; if [ -f Build ]; then buildct=`cat Build` && expr $buildct + 1 >Build; else cat 1 >Build; fi;
Don't put it in the Compile field, that way you won't waste your time incrementing the build number when gcc[++] gives errors. Hopefully there's (or will be) a plugin to do this for Geany soon, but since my Company won't update software I'd have to use this anyway.