CI: add gdc build configurations, without tests

Signed-off-by: Andrei Horodniceanu <a.horodniceanu@proton.me>

Author: the-horo

.github/workflows/main.yml

@@ -67,6 +67,9 @@ jobs:
           - dmd-2.106.1
           - dmd-2.109.1
         include:
+          - { os: ubuntu-24.04, dc: gdc-13 }
+          - { os: ubuntu-24.04, dc: gdc-14 }
+
           - { do_test: false }
           - { dc: dmd-latest, do_test: true }
           - { dc: ldc-latest, do_test: true }
@@ -103,8 +106,9 @@ jobs:
       uses: dlang-community/setup-dlang@v2
       with:
         compiler: ${{ matrix.dc }}
+        dub: latest # gdc doesn't come with dub
 
-    - name: Set DC and DMD
+    - name: Set environment variables
       shell: bash
       run: |
         for name in DC DMD; do
@@ -113,6 +117,12 @@ jobs:
           var=${var%.exe} # strip the extension
           tee -a ${GITHUB_ENV} <<<"${name}=${var}"
         done
+        # Pass -Wno-error with gdc, note that DFLAGS in the
+        # environment makes dub no longer pass -unittest on test
+        # builds so make sure tests are NOT run.
+        if [[ ${{ matrix.dc }} == gdc* ]]; then
+          tee -a ${GITHUB_ENV} <<<"DFLAGS=-Wno-error"
+        fi
 
     # Checkout the repository
     - name: Checkout