* changes:
  Update SPIRV-Tools to 9559cdbd
  Squashed 'third_party/SPIRV-Tools/' changes from d14db341b..9559cdbdf
  Update SPIRV-Headers to e4322e3b
  Squashed 'third_party/SPIRV-Headers/' changes from 79b6681aa..e4322e3be
  Temporarily disable warnings-as-errors
  Kokoro (Windows): Switch to python3