Steps to reproduce issue rust-lang/rust#53945 :

1. Edit build_good.sh and build_bad.sh with the paths to your clang, opt, and llc executeables. Note that these should be built from the same version of LLVM that Rust uses.
2. Run ./build_good.sh, and try running the produced a,out executeable
3. Run ./build_bad.sh, and note that linking fails with the __sancov_guards error message.