Yes, Clang supports FDO, but it might be hard to set up (I've never set up FDO myself). You could check out https://github.com/google/autofdo and https://clang.llvm.org/docs/UsersManual.html#profile-guided-....
(People within Google say "FDO", basically everyone else says "PGO".)
Autofdo if automatically called by the rust toolchain should alleviate the first point
https://github.com/google/autofdo
(though it only work on Linux)
How much percent slower is the build time with PGO on average?
Also worth mentioning here is perf[1], which is great for low overhead profiling. Also, perf profiles can be turned into profiles compatible with GCC and LLVM PGO to build optimized binaries based on production runs, using autofdo[2]. In my use case, the instrumentation overhead was too high to use regular profiling on production workloads.