[PATCH 1/1] utils: Adapt to llvm r325155

r325155 ("Pass a reference to a module to the bitcode writer.")
changed bit writer interface from pointer to reference

Signed-off-by: Jan Vesely <jan.vesely@rutgers.edu>

Looks ok to me. Fixes the build after I applied your 4-patch
address-space renumbering series for llvm/clang 7.

--Aaron