[clang] [llvm] Non constant size and offset in DWARF (PR #141106)

[Tom Tromey via cfe-commits]

tromey wrote:

I rebased this and fixed up the mlir problem.  I also changed how the overload resolution was done, so that a later patch that treats `nullptr` specially can be done without affecting existing call sites.

https://github.com/llvm/llvm-project/pull/141106