[clang] [llvm] Fix silent truncation of inline ASM `srcloc` cookie when going through a `DiagnosticInfoSrcMgr` (PR #84559)

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beetrees wrote:

@statham-arm I've widened the `LocCookie` in `DiagnosticInfoDontCall` as requested. I also noticed the inline ASM example in the LangRef still used an `i32` `srcloc`: while that still works fine, I updated the example to use an `i64` so that readers would be aware of the increased integer size available.

https://github.com/llvm/llvm-project/pull/84559