[workflows] Set up GitHub actions for Classic Flang

This commit squashes the following CI-related patches from the release_14x
branch.

  commit 54a96d0
  Author: Kiran Chandramohan <kiran.chandramohan@arm.com
  Date:   Wed Oct 28 17:08:22 2020 +0000

      [workflows] Removing a few CI pipelines

  commit 8bf9551
  Author: Bryan Chan <bryan.chan@huawei.com>
  Date:   Mon May 2 21:16:56 2022 -0400

      [workflows] Stop using upstream actions and enable OpenMP build

  commit b921dd2
  Author: michalpasztamobica <michal.paszta@mobica.com>
  Date:   Fri Jun 4 13:55:52 2021 +0200

      [workflows] Allow pre-compile jobs to be trigerred manually.

  commit 9f828fd
  Author: michalpasztamobica <michal.paszta@mobica.com>
  Date:   Fri Jun 4 22:09:44 2021 +0200

      [workflows] Add build scripts and make CI use them.

  commit a976b96
  Author: Abraham Tovar <abraham.tovar@mobica.com>
  Date:   Wed Oct 13 11:40:30 2021 +0200

      [workflows] LLVM release_13x CI changes

  commit 7a5ee22
  Author: Abraham Tovar <abraham.tovar@mobica.com>
  Date:   Wed Nov 17 10:14:21 2021 +0000

      [workflows] Removing CI test-base for release_100

  commit a39a0c6
  Author: pwisniewskimobica <przemyslaw.wisniewski@mobica.com>
  Date:   Thu Jan 27 15:06:19 2022 +0100

      [workflows] Use GCC 11 in CI builds

  commit 198a6b2
  Author: pwisniewskimobica <przemyslaw.wisniewski@mobica.com>
  Date:   Thu Jan 13 10:11:43 2022 +0100

      [workflows] Modify CI scripts to add more test variants

  commit 84ed34d
  Author: Bryan Chan <bryan.chan@huawei.com>
  Date:   Sun Apr 24 19:13:25 2022 -0400

      [workflows] support GitHub actions for release_14x branch

  commit dd852a6
  Author: Bryan Chan <bryanpkc@gmail.com>
  Date:   Fri Jul 15 21:50:21 2022 -0400

      [workflows] Fix CI for release_14x

  commit b52bcc0
  Author: Bryan Chan <bryanpkc@gmail.com>
  Date:   Wed Jul 27 22:28:43 2022 -0400

      [build] Stop caching AArch64 Docker image layers

.github/workflows/clang-tests.yml

@@ -32,9 +32,9 @@ concurrency:
 
 jobs:
   check_clang:
-    if: github.repository_owner == 'llvm'
-    name: Test clang,lldb,libclc
+    if: github.repository_owner == 'flang-compiler'
+    name: Test clang
     uses: ./.github/workflows/llvm-project-tests.yml
     with:
       build_target: check-clang
-      projects: clang;lldb;libclc
+      projects: clang;openmp

.github/workflows/flang-tests.yml

@@ -0,0 +1,80 @@
+name: Build and test Flang
+
+on:
+  pull_request:
+    branches: [ release_11x, release_12x, release_13x, release_14x ]
+
+jobs:
+  build:
+    runs-on: ubuntu-20.04
+    env:
+      install_prefix: /usr/local
+    strategy:
+      matrix:
+        target: [X86]
+        cc: [clang]
+        cpp: [clang++]
+        version: [10, 11]
+        include:
+          - target: X86
+            cc: gcc
+            cpp: g++
+            version: 10
+
+    steps:
+      - uses: actions/checkout@v2
+
+      - if: matrix.cc == 'clang'
+        run: |
+          sudo add-apt-repository ppa:ubuntu-toolchain-r/ppa
+          sudo touch /etc/apt/sources.list.d/llvm.list
+          echo 'deb http://apt.llvm.org/focal/ llvm-toolchain-focal-11 main' | sudo tee -a /etc/apt/sources.list.d/llvm.list
+          echo 'deb-src http://apt.llvm.org/focal/ llvm-toolchain-focal-11 main'  | sudo tee -a /etc/apt/sources.list.d/llvm.list
+          wget -q -O - http://apt.llvm.org/llvm-snapshot.gpg.key|sudo apt-key add -
+          sudo apt update
+          sudo apt install -f -y llvm-${{ matrix.version }} clang-${{ matrix.version}}
+
+      - if: matrix.cc == 'gcc' && matrix.version == '10'
+        run: |
+          sudo add-apt-repository ppa:ubuntu-toolchain-r/ppa
+          sudo apt install gcc-10 g++-10
+          sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 10
+          sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-10 20
+          sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-9 10
+          sudo update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-10 20
+
+      - name: ccache
+        uses: hendrikmuhs/ccache-action@v1
+        with:
+          key: key-${{ matrix.cc }}-${{ matrix.version }}
+
+      - name: Check tools
+        run: |
+          git --version
+          cmake --version
+          make --version
+          ${{ matrix.cc }}-${{ matrix.version }} --version
+          ${{ matrix.cpp }}-${{ matrix.version }} --version
+
+      - name: Build and install llvm
+        run: ./build-llvm-project.sh -t ${{ matrix.target }} -p ${{ env.install_prefix }} -a /usr/bin/${{ matrix.cc }}-${{ matrix.version }} -b /usr/bin/${{ matrix.cpp }}-${{ matrix.version }} -n $(nproc) -c -i -s -v
+
+      - name: Checkout flang
+        run: |
+          cd ../..
+          git clone --depth 1 --single-branch --branch master https://github.com/flang-compiler/flang.git
+
+      - name: Build and install libpgmath & flang
+        run: |
+          cd ../../flang
+          ./build-flang.sh -t ${{ matrix.target }} -p ${{ env.install_prefix }} -n $(nproc) -c -s
+
+      - name: Copy llvm-lit
+        run: |
+          cd ../../flang
+          cp ../classic-flang-llvm-project/classic-flang-llvm-project/build/bin/llvm-lit build/bin/.
+
+      - name: Test flang
+        run: |
+          cd ../../flang/build
+          make check-all