cc @ronaldoussoren @ambv

macOS 10.15.4 provides clang 11.0.3, but it seems like python.org binaries are built with Clang 6.0: https://bugs.python.org/issue41181#msg372743

While GCC had bugs with LTO a few years ago, as far as I recall, Clang always fine with LTO. PGO is a command optimization, I'm not aware of any issue with GCC or Clang.

Note: on macOS, "gcc" is a wrapper to Clang in practice:

$ gcc --version
Configured with: (...)
Apple clang version 11.0.3 (clang-1103.0.32.29)
Target: x86_64-apple-darwin19.4.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

$ clang --version
Apple clang version 11.0.3 (clang-1103.0.32.29)
Target: x86_64-apple-darwin19.4.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

Maybe the build script should be more explicit and require clang explicitly.

Thanks for the suggestion but, as discussed in the bpo issue, we are not using this option now.