add g++ to sanitizer buildbots (#1197)

.github/workflows/sanitizer.yml

@@ -5,20 +5,18 @@ on:
   pull_request: {}
 
 env:
-  CC: clang
-  CXX: clang++
-  EXTRA_CXX_FLAGS: "-stdlib=libc++"
   UBSAN_OPTIONS: "print_stacktrace=1"
 
 jobs:
   job:
-    name: ${{ matrix.sanitizer }}.${{ matrix.build_type }}
+    name: ${{ matrix.sanitizer }}.${{ matrix.build_type }}.${{ matrix.compiler }}
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
         build_type: ['Debug', 'RelWithDebInfo']
         sanitizer: ['asan', 'ubsan', 'tsan']
+        compiler: ['clang', 'gcc']
         # TODO: add 'msan' above. currently failing and needs investigation.
     steps:
     - uses: actions/checkout@v2
@@ -47,8 +45,24 @@ jobs:
         echo "EXTRA_FLAGS=-g -O2 -fno-omit-frame-pointer -fsanitize=thread -fno-sanitize-recover=all" >> $GITHUB_ENV
         echo "LIBCXX_SANITIZER=Thread" >> $GITHUB_ENV
 
+    - name: configure clang
+      if: matrix.compiler == 'clang'
+      run: |
+        echo "CC=clang" >> $GITHUB_ENV
+        echo "CXX=clang++" >> $GITHUB_ENV
+
+    - name: configure gcc
+      if: matrix.compiler == 'gcc'
+      run: |
+        sudo apt update && sudo apt -y install gcc-10 g++-10
+        echo "CC=gcc-10" >> $GITHUB_ENV
+        echo "CXX=g++-10" >> $GITHUB_ENV
+
     - name: install llvm stuff
-      run: "${GITHUB_WORKSPACE}/.github/.libcxx-setup.sh"
+      if: matrix.compiler == 'clang'
+      run: |
+        "${GITHUB_WORKSPACE}/.github/.libcxx-setup.sh"
+        echo "EXTRA_CXX_FLAGS=\"-stdlib=libc++\"" >> $GITHUB_ENV
 
     - name: create build environment
       run: cmake -E make_directory ${{ runner.workspace }}/_build