Show build environment and compiler version for Mac CI builds

This is similar to 6e96c6dda0 (Add "Show build environment" step,
2021-10-27) done for the Unix CI builds.

.github/workflows/ci_mac.yml

@@ -149,6 +149,16 @@ jobs:
         ./build/tools/before_install.sh
         mkdir -p $PWD/localbin_${{ matrix.arch }}
 
+    - name: Show build environment
+      run: |
+        echo "Environment:"
+        env | sort
+        echo
+
+        echo "Compiler version:"
+        ${CXX-g++} --version
+        echo
+
     - name: Configuring
       run: |
         wxCONFIGURE_OPTIONS="--disable-optimise $wxCONFIGURE_FLAGS"