[clang] Allow installation of Clang .cfg files if they where generated. (PR #105580)

[Vladimir Vereschaka via cfe-commits]

vvereschaka wrote:

The failed checks are related with the `std/algorithms/alg.sorting/alg.merge/pstl.merge.pass.cpp` libc++ failed test.

https://github.com/llvm/llvm-project/pull/105580