Fix a purely hypothetical problem (for now): emitWord emits in the host

Fix a purely hypothetical problem (for now): emitWord emits in the host
byte format.  This doesn't work when using the code emitter in a cross target
environment.  Since the code emitter is only really used by the JIT, this
isn't a current problem, but if we ever start emitting .o files, it would be.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@28060 91177308-0d34-0410-b5e6-96231b3b80d8