erlang: mark as always failing with llvm

There is always a better alternative than llvm-gcc available (clang on
Xcode 4.3+, gcc-4.2 elsewhere), so let's get rid of this hack (who wants
an unoptimized erlang built with llvm-gcc, anyway?)
cairo: add missing deps
erlang: disable silent rules
erlang: work around superenv bug

I don't want to bottle this quite yet since I think a fix in superenv is
imminent.

Fixes #23754.