WindowsToolchain used to download Ninja if it was specified as the CMake Generator but wasn't present on the system. That functionality was moved to WindowsCMake (to give WindowsToolchain more focused responsibilities), but #99 called out that the functionality in WindowsCMake didn't consider the Visual Studio installed version of Ninja. The responsibility of the two projects - WindowsToolchain and WindowsCMake made reconciling things difficult; WindowsToolchain is intended to be scoped and minimally sufficient, and only perform 'toolchain'-responsibilities, WindowsCMake runs 'too late' in the CMake configuration to resolve the CMAKE_MAKE_PROGRAM. This PR proposes an alternative fix - WindowsToolchain can add the location of the "Visual Studio"-installed ninja to the CMAKE_SYSTEM_PROGRAM_PATH, which CMake will consider to find the CMAKE_MAKE_PROGRAM. By appending to CMAKE_SYSTEM_PROGRAM_PATH (as opposed to, say, CMAKE_PROGRAM_PATH), the path is considered after the environment path allowing an installed ninja to be preferred.
WindowsToolchain used to download Ninja if it was specified as the CMake Generator but wasn't present on the system. That functionality was moved to WindowsCMake (to give WindowsToolchain more focused responsibilities), but #99 called out that the functionality in WindowsCMake didn't consider the Visual Studio installed version of Ninja. The responsibility of the two projects - WindowsToolchain and WindowsCMake made reconciling things difficult; WindowsToolchain is intended to be scoped and minimally sufficient, and only perform 'toolchain'-responsibilities, WindowsCMake runs 'too late' in the CMake configuration to resolve the CMAKE_MAKE_PROGRAM. This PR proposes an alternative fix - WindowsToolchain can add the location of the "Visual Studio"-installed ninja to the CMAKE_SYSTEM_PROGRAM_PATH, which CMake will consider to find the CMAKE_MAKE_PROGRAM. By appending to CMAKE_SYSTEM_PROGRAM_PATH (as opposed to, say, CMAKE_PROGRAM_PATH), the path is considered after the environment path allowing an installed ninja to be preferred.