add llvm dev package

Author: LegNeato

.github/workflows/rust.yml

@@ -84,6 +84,7 @@ jobs:
         run: |
           mkdir -p ~/llvm7 && cd ~/llvm7
           wget http://mirrors.kernel.org/ubuntu/pool/universe/l/llvm-toolchain-7/llvm-7_7.0.1-12_amd64.deb \
+               http://mirrors.kernel.org/ubuntu/pool/universe/l/llvm-toolchain-7/llvm-7-dev_7.0.1-12_amd64.deb \
                http://mirrors.kernel.org/ubuntu/pool/universe/l/llvm-toolchain-7/libllvm7_7.0.1-12_amd64.deb \
                http://mirrors.kernel.org/ubuntu/pool/universe/l/llvm-toolchain-7/llvm-7-runtime_7.0.1-12_amd64.deb
           sudo apt-get update