Auto merge of #62460 - RalfJung:llvm-null, r=eddyb

Handle null from LLVMRustGetSectionName

As part of https://github.com/rust-lang/rust/pull/58783 and https://github.com/rust-lang/rust/pull/62103, this incorrect use of a NULL pointer was found in the interface to LLVM. That PR is stuck with some linker issues, but there is no reason the soundness fix should have to wait for that.