Fix passing of structurable tuple to single Any param.

Author: cwillmor

lib/Sema/CSSimplify.cpp

@@ -516,7 +516,7 @@ matchCallArguments(ConstraintSystem &cs, TypeMatchKind kind,
     // If the param type is an empty existential composition, the function can
     // only have one argument. Check if exactly one argument was passed to this
     // function, otherwise we obviously have a mismatch
-    if (auto tupleArgType = argType->getAs<TupleType>()) {
+    if (auto tupleArgType = dyn_cast<TupleType>(argType.getPointer())) {
       if (tupleArgType->getNumElements() != 1) {
         return ConstraintSystem::SolutionKind::Error;
       }

test/Constraints/function.swift

@@ -80,3 +80,6 @@ print(r22451001(5))  // expected-error {{argument passed to call that takes no a
 func sr590(x: Any) {}
 sr590(3,4) // expected-error {{extra argument in call}}
 sr590() // expected-error {{missing argument for parameter #1 in call}}
+// Make sure calling with structural tuples still works.
+sr590(())
+sr590((1, 2))