Prioritize reducing the time to build packages, with only modest increases in the LLVM/clang build time (at least initially).

• Compile a performance team
  • Use LLVM as a backend for building team members
• Update to clang 11 once it's released, supposed to be faster
• Performance tweaks to clang/llvm
  • Reduce the number linked libs - static libc++/libc++abi/libunwind into libLLVM
    • -Wl,--as-needed to remove from clang binary
  • -mllvm -polly options for performance
  • -DENABLE_EXPERIMENTAL_NEW_PASS_MANAGER as used by most projects extending clang (testsuite is the upstream blocker)
  • Ensure -fno-semantic-interposition (this may break libc++ with clang build) and -Bsymbolic-functions in build
  • LTO (once compiler is faster) and PGO (not initially due to build time)
  • Check that tools are generating DWARFv5 by default
  • Utilise PCH where possible
    • Scan source for potential PCH capability
    • Enable in builds, Qt, LO as perfect test cases
    • Ensure -fpch-instantiate-templates is passed to the builds
• Give build tools a once over to minimize build times
  • autotools - optimize dash/bash
  • cmake
  • make
  • meson - optimize python
  • ninja
  • PCH/unity builds integrating into cmake/meson
• Integrate benchmarking-tools into boulder to make benchmarking easier (and accessible to more users)
  • General testing for impacts of core flag changes to enable by default