Fix a bugpoint crash that JeffC noticed, looking like this:

*** Attempting to perform final cleanups: Final cleanups failed.  Sorry. :(  Ple
ase report a bug!

<llc>llc.exe: bytecode didn't read correctly.
llc.exe: bytecode didn't read correctly.
<crash>
Assertion failed: M && "You can't write a null module!!", file c:\llvm\lib\bytec
ode\writer\writer.cpp, line 1094


The fact that llc bombed (in this case) is ok, but bugpoint shouldn't crash after this.

llvm-svn: 20285