Tests: Update stdlib/RuntimeObjC.swift to always link libswiftCoreGraphics.

The core definitions of CGPoint and other types were pushed down from
CoreGraphics to CoreFoundation. This test indirectly depends on the conformance
of those types to CustomReflectable, but nothing in the test was using those
conformances explicitly and so libswiftCoreGraphics would not be auto-linked
when the test is compiled at a high enough deployment target. Use the
conformances directly to force linkage.

Resolves rdar://121343931

Author: tshortli

test/stdlib/RuntimeObjC.swift

@@ -171,6 +171,11 @@ func withSwiftObjectCanary<T>(
   expectEqual(0, swiftObjectCanaryCount, stackTrace: stackTrace)
 }
 
+// Hack to ensure the CustomReflectable conformance is used directly by the test
+// in case it comes from a library that would otherwise not be autolinked.
+@inline(never)
+func assertCustomReflectable<T: CustomReflectable>(_ t: T) {}
+
 var Runtime = TestSuite("Runtime")
 
 func _isClassOrObjCExistential_Opaque<T>(_ x: T.Type) -> Bool {
@@ -614,7 +619,9 @@ Reflection.test("MetatypeMirror") {
 
 Reflection.test("CGPoint") {
   var output = ""
-  dump(CGPoint(x: 1.25, y: 2.75), to: &output)
+  let point = CGPoint(x: 1.25, y: 2.75)
+  assertCustomReflectable(point)
+  dump(point, to: &output)
 
   let expected =
     "▿ (1.25, 2.75)\n" +
@@ -626,7 +633,9 @@ Reflection.test("CGPoint") {
 
 Reflection.test("CGSize") {
   var output = ""
-  dump(CGSize(width: 1.25, height: 2.75), to: &output)
+  let size = CGSize(width: 1.25, height: 2.75)
+  assertCustomReflectable(size)
+  dump(size, to: &output)
 
   let expected =
     "▿ (1.25, 2.75)\n" +
@@ -638,11 +647,11 @@ Reflection.test("CGSize") {
 
 Reflection.test("CGRect") {
   var output = ""
-  dump(
-    CGRect(
-      origin: CGPoint(x: 1.25, y: 2.25),
-      size: CGSize(width: 10.25, height: 11.75)),
-    to: &output)
+  let rect = CGRect(
+    origin: CGPoint(x: 1.25, y: 2.25),
+    size: CGSize(width: 10.25, height: 11.75))
+  assertCustomReflectable(rect)
+  dump(rect, to: &output)
 
   let expected =
     "▿ (1.25, 2.25, 10.25, 11.75)\n" +