[clang] [clang][cmake] Move perf-training out of CLANG_INCLUDE_TESTS (PR #192163)

[Petr Hosek via cfe-commits]

petrhosek wrote:

The change itself LGTM, but the commit message seems excessive given the size of the change. Was the change generated with the help of AI? If so, it's strongly recommended that you write the commit message yourself, see https://llvm.org/docs/AIToolPolicy.html.

https://github.com/llvm/llvm-project/pull/192163