Add Clang builds to osx CI

.github/workflows/main.yaml

@@ -3,8 +3,9 @@ on: ['push', 'pull_request']
 
 jobs:
   build:
-    name: Build and Test
+    name: CI
     strategy:
+      fail-fast: false
       matrix:
         os:
           - macos-10.15
@@ -21,6 +22,22 @@ jobs:
 #           - cxx: g++-10
 #             cc: gcc-10
 #             homebrew_package: gcc@10
+          - cxx: /usr/local/opt/llvm@7/bin/clang++
+            cc: /usr/local/opt/llvm@7/bin/clang
+            homebrew_package: llvm@7
+          - cxx: /usr/local/opt/llvm@8/bin/clang++
+            cc: /usr/local/opt/llvm@8/bin/clang
+            homebrew_package: llvm@8
+          - cxx: /usr/local/opt/llvm@9/bin/clang++
+            cc: /usr/local/opt/llvm@9/bin/clang
+            homebrew_package: llvm@9
+          - cxx: /usr/local/opt/llvm@11/bin/clang++
+            cc: /usr/local/opt/llvm@11/bin/clang
+            homebrew_package: llvm@11
+          # Apple Clang
+#           - cxx: clang++
+#             cc: clang
+#             homebrew_package: ""
         build_type:
           - Debug
           - Release