Switch to focal for aarch64, update Qt

.ci/build-linux-aarch64.sh

@@ -12,8 +12,8 @@ git submodule -q update --init $(awk '/path/ && !/llvm/ { print $3 }' .gitmodule
 
 mkdir build && cd build || exit 1
 
-export CC=clang
-export CXX=clang++
+export CC="${CLANG_BINARY}"
+export CXX="${CLANGXX_BINARY}"
 
 cmake ..                                               \
     -DCMAKE_INSTALL_PREFIX=/usr                        \
@@ -27,8 +27,8 @@ cmake ..                                               \
     -DUSE_SYSTEM_FFMPEG=OFF                            \
     -DUSE_DISCORD_RPC=ON                               \
     -DOpenGL_GL_PREFERENCE=LEGACY                      \
+    -DLLVM_DIR=/opt/llvm/lib/cmake/llvm                \
     -DSTATIC_LINK_LLVM=ON                              \
-    -DBUILD_LLVM=OFF                                   \
     -G Ninja
 
 ninja; build_status=$?;