auto merge of #7409 : alexcrichton/rust/threadsafe, r=cmr

@catamorphism, this re-enables threadsafe rustpkg tests, @brson this will fail unless the bots have LLVM rebuilt, so this is a good indicator of whether that happened or not.

diff --cc src/librustc/middle/trans/base.rs
Simple merge

diff --cc src/librustpkg/tests.rs
Simple merge