llvm: enable Z3 and Zstd support.
llvm: enable Z3 and Zstd support.

This significantly improves the static analyzer. Debian also enable this
feature. See:

    https://www.cambus.net/clang-static-analyzer-and-the-z3-constraint-solver/

Zstd is used for compression of debug sections and AST serialisation.
We've enabled similar functionality in GCC. See:

    https://discourse.llvm.org/t/rfc-zstandard-as-a-second-compression-method-to-llvm/63399

Finally, enable LTO on macOS when building with PGO.

nandub/homebrew-core,adam-moss/homebrew-core,Homebrew/homebrew-core,makigumo/homebrew-core,stgraber/homebrew-core,chrisfinazzo/homebrew-core,lemzwerg/homebrew-core,Homebrew/homebrew-core,filcab/homebrew-core,nandub/homebrew-core,adam-moss/homebrew-core,chrisfinazzo/homebrew-core,filcab/homebrew-core,lemzwerg/homebrew-core,makigumo/homebrew-core,sjackman/homebrew-core,sjackman/homebrew-core,stgraber/homebrew-core