This reverts commit f37c5aa5b8.

We now know that it was not the clang version that was the problem, it
was the linker (mold)

We'll retry upgrading when clang v16 is made available.

Revert "Forgot to replace one line v14 -> 15"

This reverts commit 9d768420f6.

Revert "Bump clang from v14 to v15."

This reverts commit a9e15599dd.