Set output files path prefix for the Ninja generator.
Every output files listed in the generated
build.ninja will be prefixed by the contents of this variable (a trailing slash is appended if missing). This is useful when the generated ninja file is meant to be embedded as a
subninja file into a super ninja project. For example, a ninja build file generated with a command like:
cd top-build-dir/sub && cmake -G Ninja -DCMAKE_NINJA_OUTPUT_PATH_PREFIX=sub/ path/to/source
can be embedded in
top-build-dir/build.ninja with a directive like this:
auto-regeneration rule in
top-build-dir/build.ninja must have an order-only dependency on
CMAKE_NINJA_OUTPUT_PATH_PREFIXis set, the project generated by CMake cannot be used as a standalone project. No default targets are specified.