make extract-bc more forgiving for archives that may contain assembled objects.
make extract-bc more forgiving for archives that may contain assembled objects.

SRI-CSL/whole-program-llvm,SRI-CSL/whole-program-llvm,SRI-CSL/whole-program-llvm,SRI-CSL/whole-program-llvm,travitch/whole-program-llvm,SRI-CSL/whole-program-llvm,travitch/whole-program-llvm,travitch/whole-program-llvm,travitch/whole-program-llvm