CI updates

.github/workflows/ci.yml

@@ -68,7 +68,9 @@ jobs:
       matrix:
         include:
           - { os: ubuntu-22.04, use_m32: true }
-          - { os: ubuntu-20.04, use_m32: false } # use_m32 also works here, but save some CI time
+          - { os: ubuntu-20.04, use_m32: true } # use_m32 also works here, but save some CI time
+    env:
+      UPX_CONFIG_EXPECT_THREADS: 'ON'
     steps:
       - name: 'Install extra 32-bit and Windows packages'
         if: ${{ matrix.use_m32 }}
@@ -76,6 +78,10 @@ jobs:
           sudo dpkg --add-architecture i386
           sudo apt-get update
           sudo apt-get install -y g++-multilib g++-mingw-w64-i686 g++-mingw-w64-x86-64
+          # make sure that we use posix-threads (pthreads) and NOT win32-threads
+          for f in i686-w64-mingw32-g++ i686-w64-mingw32-gcc x86_64-w64-mingw32-g++ x86_64-w64-mingw32-gcc; do
+            if test -f /usr/bin/$f-posix; then sudo update-alternatives --set $f /usr/bin/$f-posix; fi
+          done
       - name: 'Check out code'
         uses: actions/checkout@v4
         with: { submodules: true }