[clang] [llvm] [clang][python][test] Move python binding tests to lit framework (PR #142948)

[Rainer Orth via cfe-commits]

rorth wrote:

> I reverted this in #145774 since it causes build-failures. It seems that the substitution `` CLANG_LIBRARY_PATH=`llvm-config --libdir `` doesn't work in some cases

Thanks.  When the failure reports began to trickle in, I started investigating, but it got very late.

I'd been operating under the assumption that the `llvm` part of the code is always built, which obviously isn't the case.  I strongly suspect an alternative is to create a new substitution (`%libdir`) in `lit.config.cfg`, similar to `clang/test/LibClang/lit.local.cfg`, and use that.  I'll give that a try.

What's the best way to move forward once the code is ready for review?  Is there a way to reopen this PR and augment it or do I need to create a new one?

https://github.com/llvm/llvm-project/pull/142948