libvorbis using undocumented optimization option "-O20" makes clang build fail
The optimization option "-O20" is
- Useless, because it just equals -O3
- Harmfull, because Clang (clang.llvm.org) doesn't recognize it.
It would be a very small change to patch the "-O20" to "-O3" with no change in the resulting build. It would remove undocumented behavior and allow Clang to build libvorbis (with all tests passed).