[llvm] [CI] Clean up runtimes builds (PR #131913)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

> As a follow-up for this patch, I'll make Clang Modules build reuse the build directory after C++26 build, because they only differ in LIBCXX_TEST_PARAMS (and LIBCXXABI_TEST_PARAMS). I just checked locally that we don't need a clean build to make this change propagate. This should save us couple more minutes per build (out of typical 30 minutes).

That would be great. I didn't realize we could do that.

https://github.com/llvm/llvm-project/pull/131913