When Ninja byproduct is a directory causes `clean` target to fail.
I recently added support to a project to build its API documentation .
The documentation is generated by doxygen.
I used `add_custom_command()` to run doxygen and I use `BYPRODUCTS` to
specify the output directory that will be generated by doxygen in the
hope that this would tell ninja to remove it when the `clean` target
However this doesn't work because ninja complains that the directory
Is `BYPRODUCTS` not supposed to be used with directories, or is this a bug?