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.