Ninja: do not normalise swift support file paths

When building the output-map-file.json, do not convert the path to a Ninja path, which will make it relative. If cmake is invoked with the -B option the files will be written relative to the directory where CMake was invoked rather than relative to the build tree. This path need not be a relative path since it is used internally by CMake to determine where to write the output map file. This allows the use of -B option in CMake in projects with Swift targets.

Topic-rename: ninja-swift-map-file-path