Add GCC through homebrew

Author: termoshtt

.github/workflows/openblas.yml

@@ -48,6 +48,9 @@ jobs:
       - uses: actions/checkout@v1
         with:
           submodules: 'recursive'
+      - name: Install GCC by homebrew
+        run: |
+          brew install gcc
       - name: Install OpenBLAS by homebrew
         run: |
           brew install openblas