Restored the version of LLVM that we previously

rolled back, and the testcase that the rollback
broke.

The new LLVM has a new ARM disassembler, which
may cause instability.  Keeping the old one would
force us into a contorted position vis-a-vis the
LLVM sources we bring in, so we will address
issues on the new one rather than keeping the old
one around.

llvm-svn: 138284