[llvm] [coverage] Add option for keeping mappings order (PR #91600)

[NAKAMURA Takumi via llvm-commits]

chapuni wrote:

@Lambdaris Let me ask questions.
Doesn't Rust use EXPANSION? Doesn't Rust emit FILE#>0? This is for C-family's macro expansions.

@evodius96 I guess sorting the record will prevent nested expressions. I guess sorting is not necessary if we can live with a single FILE. Could we tweak or loosen sorting?

https://github.com/llvm/llvm-project/pull/91600