[MoveChecker] Don't add defs to liveness.

When extending liveness, the instructions prior to a preexisting destroy
are added to liveness.  If that prior instruction is the def, adding it
to liveness results in multi-def liveness understanding that there is a
prior def.

Fixes a bug exposed by adding coroutine ends to liveness rather than
function ends.

Author: nate-chandler

lib/SILOptimizer/Mandatory/MoveOnlyAddressCheckerUtils.cpp

@@ -3436,8 +3436,11 @@ bool ExtendUnconsumedLiveness::hasDefAfter(SILInstruction *start,
 
 void ExtendUnconsumedLiveness::addPreviousInstructionToLiveness(
     SILInstruction *inst, unsigned element) {
-  auto range = TypeTreeLeafTypeRange(element, element + 1);
   inst->visitPriorInstructions([&](auto *prior) {
+    if (liveness.isDef(prior, element)) {
+      return true;
+    }
+    auto range = TypeTreeLeafTypeRange(element, element + 1);
     liveness.extendToNonUse(prior, range);
     return true;
   });

test/SILOptimizer/moveonly_addresschecker.sil

@@ -859,3 +859,15 @@ bb0(%0 : @guaranteed $NonTrivialStruct):
   %9999 = tuple ()
   return %9999 : $()
 }
+
+sil [ossa] @f : $@convention(thin) (@inout NonTrivialStruct, @owned NonTrivialStruct) -> () {
+entry(%out : $*NonTrivialStruct, %s : @owned $NonTrivialStruct):
+  %munc = mark_unresolved_non_copyable_value [consumable_and_assignable] %out : $*NonTrivialStruct
+  br body
+body:
+  store %s to [assign] %munc : $*NonTrivialStruct
+  br exit
+exit:
+  %retval = tuple ()
+  return %retval : $()
+}