Making GCC7 work on ubuntu 20

.github/actions/setup_gcc_ubuntu/action.yml

@@ -59,14 +59,8 @@ runs:
     - name: Install cmake via apt
       shell: bash
       run: |
-        if [[ ${{ inputs.OS == 'ubuntu:18.04' }} ]]; then
-          NAME=bionic
-        else
-          NAME=focal
-        fi
-
         wget -O - https://apt.kitware.com/keys/kitware-archive-latest.asc 2>/dev/null | gpg --dearmor - | tee /etc/apt/trusted.gpg.d/kitware.gpg >/dev/null && \
-        apt-add-repository "deb https://apt.kitware.com/ubuntu/ $NAME main" && \
+        apt-add-repository "deb https://apt.kitware.com/ubuntu/ focal main" && \
         apt update && apt install cmake -y
         apt upgrade -y
 
@@ -76,6 +70,9 @@ runs:
     - name: Install gcc
       shell: bash
       run: |
+        if [[ ${{ inputs.gcc-version == 'gcc-7' }} ]]; then
+          echo "deb http://archive.ubuntu.com/ubuntu focal main universe" >> "/etc/apt/sources.list"
+        fi
         apt-get -y install ${{ inputs.gcc-version }}
         apt-get -y install g++-$( echo ${{ inputs.gcc-version }} | cut -d '-' -f 2)
         apt update && apt upgrade -y

.github/workflows/LINUX_BUILD_TEST.yml

@@ -27,22 +27,13 @@ jobs:
       matrix:
 
         COMPILER: ['gcc-7', 'gcc-8', 'gcc-9', 'gcc-10'] # todo 'armclang'] # compiler names
-        OS: ['ubuntu:18.04','ubuntu:20.04', 'rockylinux:8', 'redhat/ubi8:latest', 'redhat/ubi9:latest', 'debian:10', 'debian:11'] # Docker images
+        OS: ['ubuntu:20.04', 'rockylinux:8', 'redhat/ubi8:latest', 'redhat/ubi9:latest', 'debian:10', 'debian:11'] # Docker images
 
         #######################################
         # Removes unecessary jobs as jobs are generated in the order seen in the matrix.
         # "Exclude" is to keep job ordering nice i.e. keeping ubuntu jobs next to each other in the list.
         #######################################
-        exclude:      
-          - OS: 'ubuntu:20.04'
-            COMPILER: 'gcc-7'
-
-          - OS: 'ubuntu:18.04'
-            COMPILER: 'gcc-8'
-          - OS: 'ubuntu:18.04'
-            COMPILER: 'gcc-9'
-          - OS: 'ubuntu:18.04'
-            COMPILER: 'gcc-10'
+        exclude:
 
           # need redhat 8 for gcc 7 and 8 | redhat 9 for gcc 9 and 10
           - OS: 'redhat/ubi8:latest'
@@ -77,16 +68,9 @@ jobs:
 
     steps:
       #######################################
-      # Clones repo to workspace. (ubuntu 18 is missing correct glibc version
-      # for newer checkout action version i.e. use older checkout version)
-      # NOTE: may want to remove support for gcc-7 soon
+      # Clones repo to workspace
       #######################################
-      - if: ${{ contains(fromJson('["ubuntu:18.04"]'), matrix.OS) }}
-        name: checkout v3
-        uses: actions/checkout@v3
-
-      - if: ${{ !contains(fromJson('["ubuntu:18.04"]'), matrix.OS) }}
-        name: checkout v4
+      - name: checkout v4
         uses: actions/checkout@v4
 
       #######################################
@@ -159,16 +143,7 @@ jobs:
       #  in the actions interface
       #######################################
 
-      - if: ${{ contains(fromJson('["ubuntu:18.04"]'), matrix.OS) && inputs.SIMENG-MODE == 'Release' }}
-        name: Checking out benchmark repository (v3)
-        uses: actions/checkout@v3
-        with:
-          repository: UoB-HPC/simeng-benchmarks
-          token: ${{ env.PAT }}
-          ref: makefile-build-system
-          path: simeng-benchmarks
-
-      - if: ${{ !contains(fromJson('["ubuntu:18.04"]'), matrix.OS) && inputs.SIMENG-MODE == 'Release' }}
+      - if: ${{ inputs.SIMENG-MODE == 'Release' }}
         name: Checking out benchmark repository (v4)
         uses: actions/checkout@v4
         with: