[llvm] [AMDGPU] Fix missing `IsExact` flag when expanding vector binary operator (PR #86712)

[Shilei Tian via llvm-commits]

shiltian wrote:

I'll update the test case in https://github.com/llvm/llvm-project/pull/83155 once that patch is landed to test this patch.

https://github.com/llvm/llvm-project/pull/86712