fix cmake-gui causing run_in_place to be always off

The boolean checkbox state for RUN_IN_PLACE seems to be cached by cmake (after using cmake-gui for the initial setup) as either "ON" or "OFF".

This value is directly used in the "cmake_config.h.in" template to generate a define, which will set RUN_IN_PLACE=ON.
Since "ON" isn't defined, subsequent makes will never build the run-in-place version, but always the user-dir-storage version.

This fix normalises the RUN_IN_PLACE value right after it's been set from the cache - maybe someone with cmake knowledge knows how to enforce the boolean to 1/0 in the first place?