getEmittedIncludeTree

pub fn getEmittedIncludeTree(cs: *Compile) LazyPath {
    if (cs.installed_headers_include_tree) |wf| return wf.getDirectory();
    const b = cs.step.owner;
    const wf = b.addWriteFiles();
    cs.installed_headers_include_tree = wf;
    for (cs.installed_headers.items) |installation| {
        cs.addHeaderInstallationToIncludeTree(installation);
    }
    // The compile step itself does not need to depend on the write files step,
    // only dependent modules do.
    return wf.getDirectory();
}