Fix infinite loop in Projection.

This was necessary for compilation purposes but was never executed. It was
caught by a clang warning.

Author: gottesmm

include/swift/SIL/Projection.h

@@ -394,7 +394,7 @@ class ProjectionPath {
   /// We only allow for moves of ProjectionPath since we only want them to be
   /// able to be constructed by calling our factory method or by going through
   /// the append function.
-  ProjectionPath(ProjectionPath &&Other) : Path(Other.Path) {}
+  ProjectionPath(ProjectionPath &&Other) : Path(std::move(Other.Path)) {}
 
   /// Append the projection P onto this.
   ProjectionPath &append(const Projection &P) {
@@ -411,8 +411,7 @@ class ProjectionPath {
   }
 
   ProjectionPath &operator=(ProjectionPath &&O) {
-    *this = std::move(O);
-    O.Path.clear();
+    std::swap(Path, O.Path);
     return *this;
   }