It's actually clang 7 not gcc 7 that we need to disable on CI, and we only need to disable it on macos. Linux can still run it.

.github/workflows/main.yaml

@@ -79,15 +79,9 @@ jobs:
         run_tests: [true]
         run_clang_tidy: [false]
         exclude:
-          # Apple CI machines cannot install GCC 7 via homebrew anymore
+          # Apple CI machines cannot install LLVM 7 via homebrew anymore
           - os: macos-10.15
-            compiler:
-              cxx: g++-7
-              cc: gcc-7
-              macos_cxx: g++-7
-              macos_cc: gcc-7
-              homebrew_package: gcc@7
-              apt_package: g++-7
+            compiler: {cxx: clang++-7, cc: clang-7, macos_cxx: /usr/local/opt/llvm@7/bin/clang++, macos_cc: /usr/local/opt/llvm@7/bin/clang, apt_package: clang-7, homebrew_package: llvm@7}
         include:
           - name: Local dependencies
             os: ubuntu-18.04