[CSApply] Use fully qualified locator while coercing ternary branches

The locator needs to much what was produced by constraint generator
otherwise Double<->CGFloat implicit coercion wouldn't be able to
find the overload choice.

Author: xedin

lib/Sema/CSApply.cpp

@@ -3735,10 +3735,12 @@ namespace {
       expr->setCondExpr(cond);
 
       // Coerce the then/else branches to the common type.
-      expr->setThenExpr(coerceToType(expr->getThenExpr(), resultTy,
-                               cs.getConstraintLocator(expr->getThenExpr())));
-      expr->setElseExpr(coerceToType(expr->getElseExpr(), resultTy,
-                                 cs.getConstraintLocator(expr->getElseExpr())));
+      expr->setThenExpr(coerceToType(
+          expr->getThenExpr(), resultTy,
+          cs.getConstraintLocator(expr, LocatorPathElt::TernaryBranch(true))));
+      expr->setElseExpr(coerceToType(
+          expr->getElseExpr(), resultTy,
+          cs.getConstraintLocator(expr, LocatorPathElt::TernaryBranch(false))));
 
       return expr;
     }

test/Constraints/implicit_double_cgfloat_conversion.swift

@@ -253,10 +253,12 @@ func assignments_with_and_without_optionals() {
     var prop: CGFloat = 0
   }
 
-  func test(c: C?, v: Double) {
+  func test(c: C?, v: Double, cgf: CGFloat) {
     c?.prop = v / 2.0 // Ok
+    c?.prop = (false ? cgf : v)
 
     let copy = c!
     copy.prop = Optional(v) ?? 0 // Ok
+    copy.prop = (true ? cgf : (false ? v : cgf))
   }
 }