Fix textproc/fcitx5-configtool ahead of KF5 5.80

I'm not sure this is really KF5 related: CMake has gotten
more conservative with #cmakedefine recently, so it might
have been missed-fallout in a CMake update previously.

No change to the port except replacing #cmakedefine
with the correct #define (the CMake variant is for variables
with boolean type at the CMake level)