[llvm] [test][DebugInfo] Fix location of test build artifacts (PR #165349)

[Jordan Rupprecht via llvm-commits]

rupprecht wrote:

> Is this fix related to https://lab.llvm.org/buildbot/#/builders/65/builds/24607?

No, that looks like a noisy test/buildbot to me.

This fix is for running this test when the current dir is not writeable.

https://github.com/llvm/llvm-project/pull/165349