[AMDGPU] Change std::sort to llvm::sort in response to r327219

[mgrang]

Summary

r327219 added wrappers to std::sort which randomly shuffle the container before sorting.
This will help in uncovering non-determinism caused due to undefined sorting
order of objects having the same key.

To make use of that infrastructure we need to invoke llvm::sort instead of std::sort.

[arsenm]

LGTM

[mgrang]

Linking back to the full patch: https://reviews.llvm.org/D44363

llvm/trunk/lib/Target/AMDGPU/GCNIterativeScheduler.cpp

|| (dbgs() << "Max RP mismatch!!!\n"
       dbgs() << "RP after scheduling: ",
       RegionMaxRP.print(dbgs(), &ST),
       false));
 }
 
 // Sort recorded regions by pressure - highest at the front
 void GCNIterativeScheduler::sortRegionsByPressure(unsigned TargetOcc) {
   const auto &ST = MF.getSubtarget<SISubtarget>();
-  std::sort(Regions.begin(), Regions.end(),
+  llvm::sort(Regions.begin(), Regions.end(),
     [&ST, TargetOcc](const Region *R1, const Region *R2) {
     return R2->MaxPressure.less(ST, R1->MaxPressure, TargetOcc);
   });
 }
 
 ///////////////////////////////////////////////////////////////////////////////
 // Legacy MaxOccupancy Strategy