[clang] [Clang][Sanitizers] Enable NSAN on X86_64 only (PR #95885)

[Alexander Shaposhnikov via cfe-commits]

alexander-shaposhnikov wrote:

yeah, but I  kind of wanted to be defensive - people will try the tool and I wanted to avoid any potential confusions / overpromises.

https://github.com/llvm/llvm-project/pull/95885