bpo-41181: macOS build script uses LTO and PGO

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The script to build the macOS installer now configures Python with
Link Time Optimization (LTO) and Profile-Guided Optimizatio (PGO).

https://bugs.python.org/issue41181

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cc @ronaldoussoren @ambv

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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.

[4383]

Nits: Optimization

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s/Profile-Guided Optimizatio/Profile-Guided Optimization/

[4383]

Commit message could be updated too (same typo)

[ned-deily]

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