[llvm] [llvm-profgen] Harden perf script invocation (PR #212253)

[Amir Ayupov via llvm-commits]

aaupov wrote:

Would it make more sense to modify PATH to replace perf binary, rather than extending command line surface? BOLT uses that model, which sidesteps passing unrelated executables as perf.

https://github.com/llvm/llvm-project/pull/212253