[ConstraintSystem] Materialize locator only once per missing argument

Instead of materializing locator twice from the same builder per
missing argument, do it only once and use result to create argument
type variable and its "defaults to Any" constraint.

Author: xedin

lib/Sema/CSSimplify.cpp

@@ -837,20 +837,20 @@ class ArgumentFailureTracker : public MatchCallArgumentListener {
     const auto &param = Parameters[paramIdx];
 
     unsigned newArgIdx = Arguments.size();
-    auto argLoc =
+    auto *argLoc = CS.getConstraintLocator(
         Locator
             .withPathElement(LocatorPathElt::ApplyArgToParam(
                 newArgIdx, paramIdx, param.getParameterFlags()))
-            .withPathElement(LocatorPathElt::SynthesizedArgument(newArgIdx));
+            .withPathElement(LocatorPathElt::SynthesizedArgument(newArgIdx)));
 
-    auto *argType = CS.createTypeVariable(
-        CS.getConstraintLocator(argLoc),
-        TVO_CanBindToInOut | TVO_CanBindToLValue | TVO_CanBindToNoEscape);
+    auto *argType =
+        CS.createTypeVariable(argLoc, TVO_CanBindToInOut | TVO_CanBindToLValue |
+                                          TVO_CanBindToNoEscape);
 
     CS.recordHole(argType);
-    CS.addUnsolvedConstraint(Constraint::create(
-        CS, ConstraintKind::Defaultable, argType, CS.getASTContext().TheAnyType,
-        CS.getConstraintLocator(argLoc)));
+    CS.addUnsolvedConstraint(
+        Constraint::create(CS, ConstraintKind::Defaultable, argType,
+                           CS.getASTContext().TheAnyType, argLoc));
 
     Arguments.push_back(param.withType(argType));
     ++NumSynthesizedArgs;