all: re-apply C++ support

.github/workflows/ci.yml

@@ -299,3 +299,20 @@ jobs:
         ./v -os windows -o /tmp/v_win.c cmd/v
         x86_64-w64-mingw32-gcc  /tmp/v_win.c -std=c99 -w -municode -o v_from_vc.exe
         ls -lart v_from_vc.exe
+
+
+
+  ubuntu-c-plus-plus:
+    runs-on: ubuntu-18.04
+    steps:
+    - uses: actions/checkout@v2
+    - name: Install dependencies
+      run: sudo rm -f /etc/apt/sources.list.d/dotnetdev.list /etc/apt/sources.list.d/microsoft-prod.list; sudo apt-get update; sudo apt-get install --quiet -y postgresql libpq-dev libglfw3 libglfw3-dev libfreetype6-dev libssl-dev sqlite3 libsqlite3-dev libsdl2-dev libsdl2-ttf-dev libsdl2-mixer-dev libsdl2-image-dev valgrind g++-9
+    - name: Build V
+      run: make -j4
+    - name: g++ version
+      run: g++-9 --version
+    - name: Running tests with g++
+      run: ./v -cc g++-9 test-fixed
+    - name: V self compilation with g++
+      run: ./v -cc g++-9 -o v2 cmd/v && ./v2 -cc g++-9 -o v3 cmd/v