CI: update the LLVM-MINGW image to a newer Clang/MingW version

This version uses msvcrt as the C runtime and not the UCRT which we can't
distribute on Win7 to Win8.1.

extras/ci/gitlab-ci.yml

@@ -14,7 +14,7 @@ default:
 variables:
     VLC_WIN32_IMAGE: registry.videolan.org/vlc-debian-win32:20200602191827
     VLC_WIN64_IMAGE: registry.videolan.org/vlc-debian-win64:20200602185103
-    VLC_WIN_LLVM_IMAGE: registry.videolan.org/vlc-debian-llvm-mingw:20190621125349
+    VLC_WIN_LLVM_IMAGE: registry.videolan.org/vlc-debian-llvm-mingw:20200603153044
     VLC_DEBIAN_IMAGE: registry.videolan.org/vlc-debian-unstable:20200229201904
     VLC_ANDROID_IMAGE: registry.videolan.org/vlc-debian-android:20190717134531
     VLC_SNAP_IMAGE: registry.videolan.org/vlc-ubuntu-bionic:20190627090437