[InstSimplify] move icmp with constant tests to another file; NFC

...because like the corresponding code, this is just too big to keep adding to.
And the next step is to add a vector version of each of these tests to show
missed folds.

Also, auto-generate CHECK lines and add comments for the tests that correspond to
the source code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@279530 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed