[llvm] [ConstantRange] Bail out early in unsignedMulMayOverflow for wide integer types (PR #192275)

[via llvm-commits]

Firebear518 wrote:

Thanks @MaxGraey and @RKSimon. Applied both suggestions in the latest commit:                                                                      
  ▎ - Added the no-overflow lower-bound check (LZ >= BitWidth → return false) as suggested by @MaxGraey. The slow path is now only reached when LZ ==  
  ▎ BitWidth-1.                                                                                                                                        
  ▎ - Added APIntTest.umul_overflows covering exhaustive 1–5-bit agreement with umul_ov, 64-bit spot checks, edge cases (0, 1, UINT64_MAX), and a      
  ▎ 2048-bit smoke test.

https://github.com/llvm/llvm-project/pull/192275