The GUI ignored a preset's installDir, so CMAKE_INSTALL_PREFIX fell back
to the platform default instead of the value the command line uses. This
fixes that by reading installDir in QCMake::properties(), and while we're
there, it applies toolchainFile after the cacheVariables loop so both
override a same-named entry.
Fixes: #27804
Daksh Mamodiya
1493cd810c