valopt nacl-cross-path "" "NaCl SDK path (Pepper Canary is recommended). Must be absolute!"
valopt release-channel "dev" "the name of the release channel to build"
valopt musl-root "/usr/local" "MUSL root installation directory"
+valopt extra-filename "" "Additional data that is hashed and passed to the -C extra-filename flag"
# Used on systems where "cc" and "ar" are unavailable
valopt default-linker "cc" "the default linker"