[llvm] [CMake] Don't explicitly set folder for InstrumentationTests (PR #170041)

[Richard Thomson via llvm-commits]

LegalizeAdulthood wrote:

> LLVM Buildbot has detected a new failure [...]

This is a compile error and I didn't change any source files or compile flags, so this doesn't appear to be related to my change.

https://github.com/llvm/llvm-project/pull/170041