https://releases.llvm.org/download.html appears to be obsolete

As of now, the page `https://releases.llvm.org/download.html` [1] only offers LLVM releases up to LLVM 18.1.8, while our _other_ download page at `https://releases.llvm.org/` [2] offers more recent version up to LLVM 21.1.0. This seems to be an oversight that should be fixed.

Note that for example the "Download" link in the sidebar of `https://clang.llvm.org/` points to `https://releases.llvm.org/download.html` (the page without the recent versions), so this actually affects some users.

[1] Screenshot of `https://releases.llvm.org/download.html`

[2] Screenshot of `https://releases.llvm.org/`