[embedded] Add swift_isUniquelyReferenced_native into the embedded runtime

Author: kubamracek

stdlib/public/core/EmbeddedRuntime.swift

@@ -146,6 +146,12 @@ func swift_initStackObject(metadata: UnsafeMutablePointer<ClassMetadata>, object
 public func swift_setDeallocating(object: Builtin.RawPointer) {
 }
 
+@_cdecl("swift_isUniquelyReferenced_native")
+public func swift_isUniquelyReferenced_native(object: Builtin.RawPointer) -> Bool {
+  if Int(Builtin.ptrtoint_Word(object)) == 0 { return false }
+  return swift_isUniquelyReferenced_nonNull_native(object: UnsafeMutablePointer<HeapObject>(object))
+}
+
 @_cdecl("swift_isUniquelyReferenced_nonNull_native")
 public func swift_isUniquelyReferenced_nonNull_native(object: Builtin.RawPointer) -> Bool {
   return swift_isUniquelyReferenced_nonNull_native(object: UnsafeMutablePointer<HeapObject>(object))

test/embedded/classes-optional.swift

@@ -0,0 +1,19 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -enable-experimental-feature Embedded -c -o %t/main.o
+// RUN: %target-clang %t/main.o -o %t/a.out -dead_strip
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: swift_in_compiler
+// REQUIRES: executable_test
+// REQUIRES: optimized_stdlib
+// REQUIRES: OS=macosx || OS=linux-gnu
+
+class Foo {
+    var foo: Foo?
+}
+
+do {
+  _ = Foo()
+  print("OK!")
+}
+// CHECK: OK!