flatpak: Use llvm14 extension
We use llvm to enable the mold linker. After the freedesktop SDK rebase, we need to use the llvm14 extension, as there is no llvm13 extension for 22.08beta.
We use llvm to enable the mold linker. After the freedesktop SDK rebase, we need to use the llvm14 extension, as there is no llvm13 extension for 22.08beta.