TempScopInfo: Microoptimize constant conditions

Use 0 >= 1 instead of 0 != 0 to represent 'false'. This might be slightly more
efficient as isl may create a union of sets for 0 != 0, whereas this is never
needed for the expression 0 >= 1.

Contributed-by: Alexandre Isoard <alexandre.isoard@gmail.com>

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@190384 91177308-0d34-0410-b5e6-96231b3b80d8