Update custom rustc instructions (#73)

.github/workflows/main.yml

@@ -31,7 +31,9 @@ jobs:
           ln gcc-build/libgccjit.so gcc-build/libgccjit.so.0
 
     - name: Set LIBRARY_PATH
-      run: echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
+      run: |
+        echo "LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
+        echo "LD_LIBRARY_PATH=$(cat gcc_path)" >> $GITHUB_ENV
 
     # https://github.com/actions/cache/issues/133
     - name: Fixup owner of ~/.cargo/
@@ -66,6 +68,7 @@ jobs:
       run: |
         ./prepare_build.sh
         ./build.sh
+        cargo test
         ./clean_all.sh
 
     - name: Prepare dependencies