[PowerPC] Do not emit HW loop if the body contains calls to lrint/lround

These two intrinsics are lowered to calls so should prevent the formation of
CTR loops. In a subsequent patch, we will handle all currently known intrinsics
and prevent the formation of HW loops if any unknown intrinsics are encountered.

Differential revision: https://reviews.llvm.org/D68841

(cherry picked from commit 97e36260)