Ninja: 1.11 will expect UTF-8 encoding on Windows

Ninja PR 1915 converts Ninja to expect UTF-8 encoding in build.ninja files when running on Windows 10 1903 or higher. CMake will need to be updated to account for this when generating build.ninja and friends.

Additionally, this comment points out that we may need to update the showIncludes prefix handling. We may need to convert the string extracted from cl's output into UTF-8 to bytewise match what is in build.ninja. There is relevant code in CMake here.