This flag ensures that the tblgen tools do not actually touch the
produced .inc file, if there are no changes to the contents. In turn,
this may prevent a number of rebuilds of files that include such .inc
files, saving build time.
While here, ensure that the shell invocations to locate the used tblgen
binary do not show unnecessary error messages.
Reported by: des
MFC after: 1 week
This uses the new layout of the upstream repository, which was recently
migrated to GitHub, and converted into a "monorepo". That is, most of
the earlier separate sub-projects with their own branches and tags were
consolidated into one top-level directory, and are now branched and
tagged together.
Updating the vendor area to match this layout is next.