The general convention for CMake is to use lowercase for commands, and
given we also follow that convention through most CMake files, this just
makes it more consistent.

The documentation for setting cache entries dicates that the type must
either be BOOL, FILEPATH, PATH, STRING, or INTERNAL (with those exact
casings). Also, given we properly case it in other places, this is just
consistent.

While we're in the same area, amend the newlining of the if block

We use spaces everywhere else in the CMake scripts, so this just makes
indentation consistent.