ci: build OpenDMARC with -std=gnu11 on macOS

Same mfapi.h bool conflict as miltertest; gcc defaults to gnu23 on this runner.

Author: thegushi

.github/workflows/ci.yml

@@ -106,7 +106,7 @@ jobs:
       - name: Configure
         run: |
           ./configure --enable-live-tests \
-            CFLAGS='-g -O2 -Wno-pointer-sign' \
+            CFLAGS='-g -O2 -Wno-pointer-sign -std=gnu11' \
             CPPFLAGS="-I$(brew --prefix openssl)/include -I/usr/local/include" \
             LDFLAGS="-L$(brew --prefix openssl)/lib -L/usr/local/lib"