[compiler-rt] Add bitmask to fix warning (#187812) After #186881 was merged the gcc libc bots started complaining about the conversion from u8 to 2 bit integer being unsafe (see: https://lab.llvm.org/buildbot/#/builders/131/builds/42788). This PR adds a bitmask that fixes the warning. GitOrigin-RevId: 6891a6ef0e2466ffb8a921d7f58934ef464f137a