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

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.

Note: This patch is one of a series of patches to replace *all* std::sort to llvm::sort.
Refer the comments section in D44363 for a list of all the required patches.

Reviewers: dblaikie, RKSimon, robertlytton

Reviewed By: robertlytton

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D44875

llvm-svn: 328564