[PATCH] [CMake][Concept] Auto dependency scanner "tddeps" for *.td

[Rafael Espíndola]

> Yes, that's what I am doing in NetBSD's LLVM build system. I have one
> pass to effectively build all the common *.inc files. I use the tblgen
> dependency output to decide when to rebuild those. If I touch one td
> file, the derived files of that file and only that file are rebuild.

Oh, not for rebuilding the .inc. This patch, if I understand it
correctly, avoids dummy dependencies in compilation units that use
.inc files.

Cheers,
Rafael