[InstCombine] update datalayout in test file; NFC

We need to specify legal integer widths to trigger PR46712,
so add those here. This doesn't appear to affect any existing
tests, and it's not clear why a datalayout would not include
any legal integer widths.

While here, change some variable names that include 'tmp' to
avoid warnings from the auto-generating script for CHECK lines.

(cherry picked from commit efc30e59)