Do not move "auto-init" instruction if they're volatile

This is overly conservative, but at least it's safe.

This is a follow-up to https://reviews.llvm.org/D137707

Author: serge-sans-paille

llvm/lib/Transforms/Utils/MoveAutoInit.cpp

@@ -109,7 +109,8 @@ static bool runMoveAutoInit(Function &F, DominatorTree &DT, MemorySSA &MSSA) {
     if (!hasAutoInitMetadata(I))
       continue;
 
-    assert(!I.isVolatile() && "auto init instructions cannot be volatile.");
+    if (I.isVolatile())
+      continue;
 
     BasicBlock *UsersDominator = usersDominator(&I, DT, MSSA);
     if (!UsersDominator)