[clang] [clang][perf-training] Support excluding LLVM build from PGO training (PR #126876)

[via cfe-commits]

Andarwinux wrote:

Just out of curiosity, is this corpus or its end product a single huge source file? If so it would also be very useful for BOLT especially instrumentation. The alternative I'm currently using is sqlite3.c

https://github.com/llvm/llvm-project/pull/126876