Silence build warnings when building afl-llvm-rt.
Silence build warnings when building afl-llvm-rt.

Would love to fix these upstream, but there is no upstream.

frewsxcv/afl.rs,frewsxcv/afl.rs,frewsxcv/afl.rs,kmcallister/afl.rs,frewsxcv/afl.rs,kmcallister/afl.rs,frewsxcv/afl.rs,frewsxcv/afl.rs,kmcallister/afl.rs,kmcallister/afl.rs,kmcallister/afl.rs,frewsxcv/afl.rs