[llvm] [CMake] Disable -Wdangling-reference warnings on GCC (PR #157541)

[Martin Storsjö via llvm-commits]

mstorsjo wrote:

> I assume this takes care of #125544, #125542, #125538.

Yes, it seems so.

> Should probably get some upstream bug report as well otherwise it will never improve.

Yes, ideally... Do you feel like writing a report? I see that you had some analysis in https://github.com/llvm/llvm-project/issues/125538 already. The example I outline in the commit message here also is quite clear, both in why it isn't an issue, but also why it's understandably hard for the compiler to know whether it is an issue or not.

https://github.com/llvm/llvm-project/pull/157541