compiler_rt: declutter int.zig, add mulXi3 tests (#14623)

- Combine mulXi3 routines for follow-up cleanup.
- DRY up Dwords and Twords
- rename both to HalveInt and use instance
  * Justification: Not all processors have word size 32 bit.
* remove test file from CMakeLists
* DRY things.
97b9facb98matu3ba committed on 2/24/2023, 6:27:02 PM· committed by GitHubparent5f70c36
11 files changedLine totals unavailable