Add gcc11 to Ubuntu20.04 setup and add PkgConfig install

Modernize the compiler used on Ubuntu 20.04. Once Velox moves to using the
C++20 standard the system gcc9 compiler cannot be used anymore.

In addition, recent upgrades added the usage of PkgConfig which was not installed into the system and is
not by default pre-installed into ubuntu 20.04.

scripts/setup-ubuntu.sh

@@ -41,9 +41,16 @@ SUDO="${SUDO:-"sudo --preserve-env"}"
 USE_CLANG="${USE_CLANG:-false}"
 export INSTALL_PREFIX=${INSTALL_PREFIX:-"/usr/local"}
 DEPENDENCY_DIR=${DEPENDENCY_DIR:-$(pwd)/deps-download}
+VERSION=$(cat /etc/os-release | grep VERSION_ID)
+
+# On Ubuntu 20.04 dependencies need to be built using gcc11.
+# On Ubuntu 22.04 gcc11 is already the system gcc installed.
+if [[ ${VERSION} =~ "20.04" ]]; then
+  export CC=/usr/bin/gcc-11
+  export CXX=/usr/bin/g++-11
+fi
 
 function install_clang15 {
-  VERSION=`cat /etc/os-release | grep VERSION_ID`
   if [[ ! ${VERSION} =~ "22.04" && ! ${VERSION} =~ "24.04" ]]; then
     echo "Warning: using the Clang configuration is for Ubuntu 22.04 and 24.04. Errors might occur."
   fi
@@ -54,6 +61,15 @@ function install_clang15 {
   ${SUDO} apt install ${CLANG_PACKAGE_LIST} -y
 }
 
+# For Ubuntu 20.04 we need add the toolchain PPA to get access to gcc11.
+function install_gcc11_if_needed {
+  if [[ ${VERSION} =~ "20.04" ]]; then
+    ${SUDO} add-apt-repository ppa:ubuntu-toolchain-r/test -y
+    ${SUDO} apt update
+    ${SUDO} apt install gcc-11 g++-11 -y
+  fi
+}
+
 FB_OS_VERSION="v2024.07.01.00"
 FMT_VERSION="10.1.1"
 BOOST_VERSION="boost-1.84.0"
@@ -75,14 +91,18 @@ function install_build_prerequisites {
     ninja-build \
     checkinstall \
     git \
+    pkg-config \
     wget
 
   # Install to /usr/local to make it available to all users.
   ${SUDO} pip3 install cmake==3.28.3
 
+  install_gcc11_if_needed
+
   if [[ ${USE_CLANG} != "false" ]]; then
     install_clang15
   fi
+
 }
 
 # Install packages required for build.
@@ -294,6 +314,11 @@ function install_apt_deps {
       echo "  export CC=/usr/bin/clang-15"
       echo "  export CXX=/usr/bin/clang++-15"
     fi
+    if [[ ${VERSION} =~ "20.04" && ${USE_CLANG} == "false" ]]; then
+      echo "To build Velox gcc-11/g++11 is required. Set the CC and CXX environment variables in your session."
+      echo "  export CC=/usr/bin/gcc-11"
+      echo "  export CXX=/usr/bin/g++-11"
+    fi
   fi
 )