Specify the default startup project in a Visual Studio solution.

The Visual Studio Generators create a .sln file for each directory whose CMakeLists.txt file calls the project() command. Set this property in the same directory as a project() command call (e.g. in the top-level CMakeLists.txt file) to specify the default startup project for the correpsonding solution file.

The property must be set to the name of an existing target. This will cause that project to be listed first in the generated solution file causing Visual Studio to make it the startup project if the solution has never been opened before.

If this property is not specified, then the ALL_BUILD project will be the default.