[clang] [clang] Add missing BuiltinAnchorSources.def to module map (PR #200125)

[Balázs Benics via cfe-commits]

https://github.com/steakhal approved this pull request.

Ouch, thanks for spotting.
How did I miss this?
I was looking for build bot failures, but I can't recally anything relevant.

https://github.com/llvm/llvm-project/pull/200125