[lld] r185657 - Don't pass llvm::errs() all over the place. Diagnostics always go to stderr.

[Rafael Espíndola]

> There are unittests in lld that run invoke the Drivers with raw_string_ostreams and parse the string to check that the correct error was generated.  This change breaks those tests.
>
> I just recently noticed that those unittests are not being built and run as part of the lld-test target.  I’m still trying to figure out why.

OK, if we need these tests, then we should revert this, but may I ask
what is wrong with with pipes + FileCheck? That is how we test every
error other than clang's -verify support.

> -Nick
>

Cheers,
Rafael