Don’t make the install target depend on the all target.

By default, the “install” target depends on the “all” target. This has the effect, that when “make install” is invoked or INSTALL is built, first the “all” target is built, then the installation starts. If CMAKE_SKIP_INSTALL_ALL_DEPENDENCY is set to TRUE, this dependency is not created, so the installation process will start immediately, independent from whether the project has been completely built or not.