- Don't need an extra indirection from WITH_KF5Crash to WITH_KCRASH,
just use the cmakedefine directly.
- Since the setting is only used in main.cpp, move the define
down there and remove cmakedefine entirely.
Honor SYSCONFDIR as specified by CMake arguments instead of
using a hard-coded path.
Since GNUInstallDirs set CMAKE_INSTALL_FULL_SYSCONFDIR to
CMAKE_INSTALL_PREFIX/etc we need to change the default ourselves.
