GHA: add a gcc-11 -O3 build using OpenSSL

Since -O3 might trigger other warnings

Closes #9454

.github/workflows/openssl3.yml

@@ -30,11 +30,15 @@ jobs:
         - name: openssl3-clang
           install: libpsl-dev libbrotli-dev libzstd-dev zlib1g-dev clang
           configure: CC=clang LDFLAGS="-Wl,-rpath,$HOME/openssl3/lib64" --with-openssl=$HOME/openssl3 --enable-debug
+        - name: openssl3-O3
+          install: libpsl-dev libbrotli-dev libzstd-dev zlib1g-dev
+          configure: CFLAGS=-O3 LDFLAGS="-Wl,-rpath,$HOME/openssl3/lib64" --with-openssl=$HOME/openssl3 --enable-debug
 
     steps:
     - run: |
+        sudo add-apt-repository ppa:ubuntu-toolchain-r/ppa
         sudo apt-get update
-        sudo apt-get install libtool autoconf automake pkg-config stunnel4 ${{ matrix.build.install }}
+        sudo apt-get install libtool autoconf automake pkg-config stunnel4 ${{ matrix.build.install }} gcc-11
         sudo python3 -m pip install impacket
       name: 'install prereqs and impacket'
 
@@ -47,6 +51,14 @@ jobs:
 
     - uses: actions/checkout@v3
 
+    - run: |
+        sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-11 100
+        sudo update-alternatives --set gcc /usr/bin/gcc-11
+      name: 'switch to gcc-11'
+
+    - run: gcc --version
+      name: 'check gcc version'
+
     - run: autoreconf -fi
       name: 'autoreconf'