Use a newer docker image for cmake build (#7958)

Xenial is outdated and the ca-certs no longer work.
# Conflicts:
#	Jenkinsfile
resolved with accept both

.CI/cache-without-cmake/Dockerfile

@@ -0,0 +1,7 @@
+# Cannot be parametrized in Jenkins...
+FROM docker.openmodelica.org/build-deps:v1.16.3
+
+# We don't know the uid of the user who will build, so make the /cache directories world writable
+
+RUN mkdir -p /cache/runtest/ /cache/omlibrary/ && chmod ugo+rwx /cache/runtest/ /cache/omlibrary/ \
+    && apt-get remove -qy cmake cmake-data

Jenkinsfile

@@ -176,6 +176,41 @@ pipeline {
             //stash name: 'omc-centos7', includes: 'build/**, **/config.status'
           }
         }
+        stage('cmake-gcc') {
+          agent {
+            dockerfile {
+              additionalBuildArgs '--pull'
+              dir '.CI/cache-without-cmake'
+              label 'linux'
+              args "-v /var/lib/jenkins/gitcache:/var/lib/jenkins/gitcache"
+              args "--mount type=volume,source=omlibrary-cache,target=/cache/omlibrary " +
+                   "-v /var/lib/jenkins/gitcache:/var/lib/jenkins/gitcache"
+            }
+          }
+          when {
+            beforeAgent true
+            expression { !shouldWeSkipCMakeBuild_value }
+          }
+          environment {
+            CC = "gcc-5"
+            CXX = "g++-5"
+          }
+          steps {
+            script {
+              echo "Download and install CMake 3.17.2"
+              sh '''
+                wget "cmake.org/files/v3.17/cmake-3.17.2-Linux-x86_64.sh"
+                mkdir -p /tmp/cmake
+                sh cmake-3.17.2-Linux-x86_64.sh --prefix=/tmp/cmake --skip-license
+                /tmp/cmake/bin/cmake --version
+              '''
+              common.buildOMC_CMake('-DCMAKE_BUILD_TYPE=Release -DOMC_USE_CCACHE=OFF -DCMAKE_INSTALL_PREFIX=build', '/tmp/cmake/bin/cmake')
+              sh "build/bin/omc --help"
+              sh "build/bin/omc --version"
+            }
+            // stash name: 'omc-cmake-gcc', includes: 'OMCompiler/build_cmake/install_cmake/bin/**'
+          }
+        }
         stage('checks') {
           agent {
             docker {