Add clang passing build

CircleCI Xenial does not come with an up to date version of Clang. It is
therefore required to get the newest version (8). The .pri file has
quickly been edited to be similar to the g++ version check.

.circleci/config.yml

@@ -1,6 +1,14 @@
-version: 2
+workflows:
+    version: 2
+    gcc_1:
+        jobs:
+          - gcc
+    clang_1:
+        jobs:
+          - clang
+
 jobs:
-    build:
+    gcc:
         docker:
             - image: "ubuntu:xenial"
         steps:
@@ -47,4 +55,53 @@ jobs:
             - run:
                 name: Run build script
                 command: './build_scripts/linux/build_linux.sh'
-
+    clang:
+        docker:
+            - image: circleci/buildpack-deps:xenial
+        steps:
+            - checkout
+            - run:
+                name: Set up env vars
+                command: echo 'export QMAKE_SPEC=linux-clang' >> $BASH_ENV; echo 'export QT_SELECT=opt-qt512' >> $BASH_ENV
+            - run:
+                name: Update and upgrade
+                command: 'sudo apt-get update && sudo apt-get upgrade -y'
+            - run:
+                name: Get wget
+                command: 'sudo  apt-get install wget -y; sudo  apt-get install software-properties-common -y'
+            - run:
+                name: Prereqs for clang-format-8
+                command: wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo  apt-key add -; sudo  add-apt-repository 'deb http://apt.llvm.org/xenial/ llvm-toolchain-xenial-8 main'
+            - run:
+                name: Installing clang-format-8
+                command: ' sudo apt update -qq;  sudo apt install clang-format-8 -y; sudo clang-format-8 --version;'
+            - run:
+                name: Installing clang-8
+                command: 'sudo apt install clang-8 -y; sudo apt install clang -y; clang++ --version;'
+            - run:
+                name: Run clang-format
+                command: 'python ./build_scripts/run-clang-format.py ./src -r --color always --clang-format-executable clang-format-8'
+            - run:
+                name: Install g++-7
+                command: sudo apt-get install -y software-properties-common; sudo add-apt-repository ppa:ubuntu-toolchain-r/test; sudo apt update; sudo apt install g++-7 -y;
+            - run:
+                name: Install required packages
+                command: 'sudo  add-apt-repository ppa:kubuntu-ppa/backports -y;  sudo add-apt-repository ppa:beineri/opt-qt-5.12.2-xenial -y;  sudo apt-get update -qq;  sudo apt-get install build-essential libgl1-mesa-dev -y'
+            - run:
+                name: Install QT packages
+                command: 'sudo apt-get install qt512-meta-minimal qt512multimedia qt512declarative qt512quickcontrols2  qt512tools  qt512base qtchooser -y'
+            - run:
+                name: Install X11 packages
+                command: ' sudo apt-get install libx11-dev libxt-dev libxtst-dev -y'
+            - run:
+                name: Install bear/clang-tidy
+                command: ' sudo apt-get install bear clang-tidy -y'
+            - run:
+                name: Set up QT
+                command: 'qtchooser -install opt-qt512 /opt/qt512/bin/qmake'
+            - run:
+                name: Give build scripts +x
+                command: 'chmod +x ./build_scripts/linux/build_linux.sh; chmod +x ./build_scripts/linux/format.sh; chmod +x ./build_scripts/linux/run-clang-tidy.sh ;chmod +x ./build_scripts/linux/verify_formatting.sh'
+            - run:
+                name: Run build script
+                command: './build_scripts/linux/build_linux.sh'

build_scripts/qt/compilers/clang.pri

@@ -1,3 +1,16 @@
+# Makes sure the "clang++" command used to invoke the compilation is abvove version 8.
+# If it's at or above version 7 then we can use the default clang++ otherwise we'll
+# specifically need clang++-8.
+CLANG_VERSION = $$system("clang++ -dumpversion")
+!greaterThan(CLANG_VERSION, 7) {
+    message('clang++' version is not above 8. Manually using 'clang++-8'.)
+    !system(clang++-8 --version) {
+        error(At least clang++-8 required.)
+    }
+    #clang++-8 is needed for C++17 features. travis does not supply this by default.
+    QMAKE_CXX = clang++-8
+}
+
 include(clang-gcc-common-switches.pri)
 
 QMAKE_CXXFLAGS += -Wmost