diff --git a/.github/actions/1-setup/action.yml b/.github/actions/1-setup/action.yml
index 6b98463e3664112..26e92a4023a00f3 100644
--- a/.github/actions/1-setup/action.yml
+++ b/.github/actions/1-setup/action.yml
@@ -1,7 +1,5 @@
 name: Install prerequisites
 inputs:
-  clang_version:
-    required: true
   arch:
     required: true
 runs:
@@ -17,50 +15,43 @@ runs:
         export DEBIAN_FRONTEND=noninteractive
         sudo apt-get -q update
         sudo -E apt-get -yq install \
-          git-core curl xz-utils ninja-build g++ python3 pkgconf binutils-dev libxml2-dev libzstd-dev zlib1g-dev p7zip-full unzip
+          git-core curl xz-utils g++ python3 pkgconf binutils-dev libxml2-dev libzstd-dev zlib1g-dev p7zip-full unzip
 
-        # install a recent CMake version (Ubuntu 20's too old)
-        curl -fL --retry 3 --max-time 300 -o cmake.tar.gz \
-          https://github.com/Kitware/CMake/releases/download/v3.31.4/cmake-3.31.4-linux-${{ inputs.arch }}.tar.gz
-        mkdir cmake
-        tar -xf cmake.tar.gz --strip 1 -C cmake
-        rm cmake.tar.gz
-        sudo ln -sf $PWD/cmake/bin/cmake /usr/bin/cmake
+        # install a more recent CMake version in the AArch64 container (Ubuntu 20's too old)
+        if [[ $arch == aarch64 ]]; then
+          curl -fL --retry 3 --max-time 300 -o cmake.tar.gz \
+            https://github.com/Kitware/CMake/releases/download/v3.31.4/cmake-3.31.4-linux-${{ inputs.arch }}.tar.gz
+          mkdir cmake
+          tar -xf cmake.tar.gz --strip 1 -C cmake
+          rm cmake.tar.gz
+          sudo ln -sf $PWD/cmake/bin/cmake /usr/bin/cmake
+        fi
 
-    - name: 'Linux: Download & extract clang' # into ../clang
+    - name: 'Linux: Install clang 19 from apt.llvm.org'
       if: runner.os == 'Linux'
       shell: bash
       run: |
         set -eux
         cd ..
-        version='${{ inputs.clang_version }}'
-        arch='${{ inputs.arch }}'
-        extraSuffix=''
-        if [[ $arch == x86_64 ]]; then
-          extraSuffix='-ubuntu-18.04'
-        fi
-        curl -fL --retry 3 --max-time 300 -o clang.tar.xz \
-          https://github.com/llvm/llvm-project/releases/download/llvmorg-$version/clang+llvm-$version-$arch-linux-gnu$extraSuffix.tar.xz
-        mkdir clang
-        tar -xf clang.tar.xz --strip 1 -C clang
-        rm clang.tar.xz
-        clang/bin/clang --version
+        curl -fL --retry 3 --max-time 30 -O https://apt.llvm.org/llvm.sh
+        sudo bash llvm.sh 19
 
         # use it as C(++) compiler for future steps
-        echo "CC=$PWD/clang/bin/clang" >> $GITHUB_ENV
-        echo "CXX=$PWD/clang/bin/clang++" >> $GITHUB_ENV
+        echo "CC=clang-19" >> $GITHUB_ENV
+        echo "CXX=clang++-19" >> $GITHUB_ENV
 
         # make bundled lld the default linker
-        sudo ln -sf "$PWD/clang/bin/ld.lld" /usr/bin/ld
+        sudo ln -sf ld.lld-19 /usr/bin/ld
         ld --version
-    - name: 'Windows: Install clang'
+
+    - name: 'Windows: Install clang v19.1.3 from GitHub'
       if: runner.os == 'Windows'
       shell: bash
       run: |
         set -eux
         cd ..
         curl -fL --retry 3 --max-time 300 -o clang.exe \
-          https://github.com/llvm/llvm-project/releases/download/llvmorg-${{ inputs.clang_version }}/LLVM-${{ inputs.clang_version }}-win64.exe
+          https://github.com/llvm/llvm-project/releases/download/llvmorg-19.1.3/LLVM-19.1.3-win64.exe
         ./clang.exe //S # double-slash for bash
         rm clang.exe
 
@@ -78,9 +69,8 @@ runs:
           echo "ASMFLAGS=-m32" >> $GITHUB_ENV
         fi
 
-    - name: 'Non-Linux: Install ninja'
-      if: runner.os != 'Linux'
-      uses: seanmiddleditch/gha-setup-ninja@v4
+    - name: Install ninja v1.12.1
+      uses: Ahajha/gha-setup-ninja@69595b0cf872acdad8ce599142fbdc88724b9a2b
 
     - name: 'Windows: Set LDC_VSDIR env variable'
       if: runner.os == 'Windows'
diff --git a/.github/workflows/ldc-release.yml b/.github/workflows/ldc-release.yml
index 1c62f8a0ebed5d3..1e508f7352bf7c2 100644
--- a/.github/workflows/ldc-release.yml
+++ b/.github/workflows/ldc-release.yml
@@ -11,8 +11,6 @@ concurrency:
   cancel-in-progress: true
 
 env:
-  # no recent official clang packages for Ubuntu 20
-  CLANG_VERSION: 15.0.6
   # Prevent dependencies on some purely optional libraries, and a dependency on clang
   # for compiler-rt tests.
   BASE_CMAKE_FLAGS: >-
@@ -33,22 +31,18 @@ jobs:
             os: windows-2022
             arch: x64
             with_asserts: false
-            clang_version: 19.1.3 # the MSVC headers require clang 16+
           - job_name: Windows x64 withAsserts
             os: windows-2022
             arch: x64
             with_asserts: true
-            clang_version: 19.1.3 # the MSVC headers require clang 16+
           - job_name: Windows x86
             os: windows-2022
             arch: x86
             with_asserts: false
-            clang_version: 19.1.3 # the MSVC headers require clang 16+
           - job_name: Windows x86 withAsserts
             os: windows-2022
             arch: x86
             with_asserts: true
-            clang_version: 19.1.3 # the MSVC headers require clang 16+
           - job_name: Linux x86_64
             os: ubuntu-20.04
             arch: x86_64
@@ -62,13 +56,11 @@ jobs:
             container_image: ubuntu:20.04
             arch: aarch64
             with_asserts: false
-            clang_version: 15.0.3 # 15.0.6 requires a more recent libstdc++.so.6 than shipped with Ubuntu 20
           - job_name: Linux aarch64 withAsserts
             os: ubuntu-22.04-arm # Ubuntu 20 not natively supported
             container_image: ubuntu:20.04
             arch: aarch64
             with_asserts: true
-            clang_version: 15.0.3 # 15.0.6 requires a more recent libstdc++.so.6 than shipped with Ubuntu 20
           - job_name: macOS arm64
             os: macos-15
             arch: arm64
@@ -103,7 +95,6 @@ jobs:
       - name: Install prerequisites
         uses: ./.github/actions/1-setup
         with:
-          clang_version: ${{ matrix.clang_version || env.CLANG_VERSION }}
           arch: ${{ matrix.arch }}
       # BOLT supports ELF binaries only, so include it for Linux packages only
       - name: Build & install LLVM incl. LLD, compiler-rt${{ runner.os == 'Linux' && ', BOLT' || '' }}
@@ -156,7 +147,6 @@ jobs:
       - name: Install prerequisites
         uses: ./.github/actions/1-setup
         with:
-          clang_version: ${{ env.CLANG_VERSION }}
           arch: x86_64
       - name: Build native llvm-tblgen
         shell: bash