[clang] [ubsan] Use SanitizerOrdinal instead of SanitizerMask for EmitCheck (exactly one sanitizer is required) (PR #122511)

[Vitaly Buka via cfe-commits]

vitalybuka wrote:

I would describe reason as "to avoid ambiguity in EmitCheck about what to do if multiple bits are set".
But your description is OK as well.

https://github.com/llvm/llvm-project/pull/122511