8256277: Github Action build on macOS should define OS and Xcode versions

Reviewed-by: shade, ehelin, erikj

Author: rwestberg

.github/workflows/submit.yml

@@ -1543,7 +1543,7 @@ jobs:
 
   macos_x64_build:
     name: macOS x64
-    runs-on: "macos-latest"
+    runs-on: "macos-10.15"
     needs: prerequisites
     if: needs.prerequisites.outputs.should_run != 'false' && needs.prerequisites.outputs.platform_macos_x64 != 'false'
 
@@ -1613,6 +1613,9 @@ jobs:
       - name: Install dependencies
         run: brew install make
 
+      - name: Select Xcode version
+        run: sudo xcode-select --switch /Applications/Xcode_11.3.1.app/Contents/Developer
+
       - name: Configure
         run: >
           bash configure
@@ -1643,7 +1646,7 @@ jobs:
 
   macos_x64_test:
     name: macOS x64
-    runs-on: "macos-latest"
+    runs-on: "macos-10.15"
     needs:
       - prerequisites
       - macos_x64_build
@@ -1756,6 +1759,9 @@ jobs:
       - name: Install dependencies
         run: brew install make
 
+      - name: Select Xcode version
+        run: sudo xcode-select --switch /Applications/Xcode_11.3.1.app/Contents/Developer
+
       - name: Find root of jdk image dir
         run: |
           imageroot=`find ${HOME}/jdk-macos-x64${{ matrix.artifact }}/jdk-${{ env.JDK_VERSION }}-internal+0_osx-x64_bin${{ matrix.artifact }} -name release -type f`