Move -Wno-error-dangling-reference to common.h GCC pragma

Only GCC 13+ recognizes it, seems simpler to add it to `common.h`'s opening list of known-spurious warnings we disable to build cppfront cleanly

Author: hsutter

.github/workflows/build-cppfront.yaml

@@ -42,7 +42,7 @@ jobs:
     runs-on: ${{ matrix.runs-on }}
     env:
       CXX: ${{ matrix.compiler }}
-      CXXFLAGS: -std=${{ matrix.cxx-std }} -Wall -Wextra -Wold-style-cast -Wunused-parameter -Wno-error=dangling-reference -Wpedantic -Werror -pthread
+      CXXFLAGS: -std=${{ matrix.cxx-std }} -Wall -Wextra -Wold-style-cast -Wunused-parameter -Wpedantic -Werror -pthread
     steps:
     - uses: actions/checkout@v3
     - name: Install compiler

source/common.h

@@ -11,8 +11,13 @@
 // THE SOFTWARE.
 
 
+//  We want cppfront to build cleanly at very high warning levels, with warnings
+//  as errors -- so disable a handful that fire incorrectly due to compiler bugs
 #ifdef _MSC_VER
-#pragma warning(disable: 4456)
+    #pragma warning(disable: 4456)
+#endif
+#if defined(__GNUC__) && __GNUC__ >= 13 && !defined(__clang_major__)
+    #pragma GCC diagnostic ignored "-Wno-dangling-reference"
 #endif
 
 #include "cpp2util.h"