[LV/LAA] Avoid specializing a loop for stride=1 when this predicate implies a
single-iteration loop

This fixes PR34681. Avoid adding the "Stride == 1" predicate when we know that
Stride >= Trip-Count. Such a predicate will effectively optimize a single
or zero iteration loop, as Trip-Count <= Stride == 1.

Differential Revision: https://reviews.llvm.org/D38785

llvm-svn: 317438