This will link to std and compile with the --test flag. Eventually the
run-pass/lib* tests will move here.

We could also put the std tests directly into the library and compile both a
library version and a test version, but I think this way will make for faster
builds.

Issue #428

The tinderbox snapshotting scripts seem to be looking for a stage2-check
target when they should be using check-stage2. Since Graydon is out of the
office, I'm making this change to see if the snapshot will go through.

There's even more duplication now, but I'm reluctant to touch it since it's
easy to subtly break the build rules

rustc.exe.exe.

in getting a driver that works on all linux systems.

Sorry for the linker hacks, I will remove them after snapshotting a new compiler.

This is no longer necessary since error logging is not affected by RUST_LOG.

A typo in the Makefile was causing these to not run. Happily, a lot of these
tests pass, so un-xfailed.

Fix horrible rule-hijacking bug that was causing compile-fail targets to trigger honest compile attempts.