Bug#1050071: llvm-defaults: move to 16

[Simon McVittie]

On Sat, 19 Aug 2023 at 10:39:44 +0200, Sylvestre Ledru wrote:
> llvm-defaults has been pointing to 16 in experimental for quite sometime.
> Opening this transition to make sure it is on your radar! :)
> 
> I opened bug #1050070 & #1050069 for future removals.

Mesa is a significant user of LLVM, and hard-codes its own non-default
version of LLVM which often runs ahead of the default (currently 15).
It seems to be relatively common for a LLVM version upgrade to cause
regressions or uninstallability on at least one architecture, and also
relatively common for a LLVM version upgrade to be necessary to unblock
features or bug fixes in Mesa, which I assume is why the Mesa maintainers
have felt the need to control this themselves.

Should Mesa try moving to -16 *before* the default changes? It would
seem unhelpful to move the rest of the distribution to a version that
Mesa can't use for whatever reason.

I've opened a Mesa bug at wishlist severity suggesting a move to version
16, and set it to block the bug for llvm-toolchain-15 removal (#1050070).

    smcv