To run the libbcc lit tests:
* Ensure `llvm-rs-as` is built, either by doing a top-level `make
checkbuild` or by doing `mm` from frameworks/compile/slang.
* Ensure that LLVM and libbcc are built with
`FORCE_BUILD_LLVM_COMPONENTS=true`.
* Ensure `opt` is built from external/llvm, either by top-level `make
checkbuild` or by doing `mm` from external/llvm.