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

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.

llvm-svn: 328636
diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 4cc3f9c..d77760d 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -396,8 +396,8 @@
                                              ExistingTargetOpts.FeaturesAsWritten.end());
   SmallVector<StringRef, 4> ReadFeatures(TargetOpts.FeaturesAsWritten.begin(),
                                          TargetOpts.FeaturesAsWritten.end());
-  std::sort(ExistingFeatures.begin(), ExistingFeatures.end());
-  std::sort(ReadFeatures.begin(), ReadFeatures.end());
+  llvm::sort(ExistingFeatures.begin(), ExistingFeatures.end());
+  llvm::sort(ReadFeatures.begin(), ReadFeatures.end());
 
   // We compute the set difference in both directions explicitly so that we can
   // diagnose the differences differently.
@@ -9078,8 +9078,8 @@
   NextCursor:
     // De-serialized SourceLocations get negative FileIDs for other modules,
     // potentially invalidating the original order. Sort it again.
-    std::sort(Comments.begin(), Comments.end(),
-              BeforeThanCompare<RawComment>(SourceMgr));
+    llvm::sort(Comments.begin(), Comments.end(),
+               BeforeThanCompare<RawComment>(SourceMgr));
     Context.Comments.addDeserializedComments(Comments);
   }
 }