Support singleton objects in C interop. (#1940)

backend.native/tests/build.gradle

@@ -2896,6 +2896,7 @@ task produce_dynamic(type: DynamicKonanTest) {
                 "RW property is 239\n" +
                 "enum100 = 100\n" +
                 "object = 42\n" +
+                "singleton = I am single\n" +
                 "topLevel = 777 3\n"
 }
 

backend.native/tests/produce_dynamic/simple/hello.kt

@@ -45,6 +45,10 @@ val an_object = object : Codeable {
     override fun asCode() = 42
 }
 
+object Singleton {
+    override fun toString() = "I am single"
+}
+
 class Child : Base() {
     override fun fooParam(arg0: String, arg1: Int) = println("Child.fooParam: $arg0 $arg1")
 

backend.native/tests/produce_dynamic/simple/main.c

@@ -15,8 +15,10 @@ int main(void) {
     T_(I) casted_impl2 = { .pinned = impl2.pinned };
     T_(Enum) enum1 = __ kotlin.root.Enum.HUNDRED.get();
     T_(Codeable) object1 = __ kotlin.root.get_an_object();
+    T_(Singleton) singleton = __ kotlin.root.Singleton._instance();
 
-    const char* string = __ kotlin.root.getString();
+    const char* string1 = __ kotlin.root.getString();
+    const char* string2 = __ kotlin.root.Singleton.toString(singleton);
 
     __ kotlin.root.hello();
     __ kotlin.root.Base.foo(base);
@@ -26,7 +28,7 @@ int main(void) {
     __ kotlin.root.I.foo(casted_impl1, "d", 4, casted_impl1);
     __ kotlin.root.I.foo(casted_impl2, "e", 5, casted_impl2);
 
-    printf("String is %s\n", string);
+    printf("String is %s\n", string1);
 
     printf("RO property is %d\n", __ kotlin.root.Child.get_roProperty(child));
      __ kotlin.root.Child.set_rwProperty(child, 238);
@@ -36,13 +38,17 @@ int main(void) {
 
     printf("object = %d\n",  __ kotlin.root.Codeable.asCode(object1));
 
+    printf("singleton = %s\n",  string2);
+
     topLevelFunctionVoidFromC(42, 0);
     __ kotlin.root.topLevelFunctionVoid(42, 0);
     printf("topLevel = %d %d\n", topLevelFunctionFromC(780, 3), __ kotlin.root.topLevelFunctionFromCShort(5, 2));
 
     __ kotlin.root.useInlineClasses(42, "bar", base);
 
-    __ DisposeString(string);
+    __ DisposeStablePointer(singleton.pinned);
+    __ DisposeString(string1);
+    __ DisposeString(string2);
     __ DisposeStablePointer(base.pinned);
     __ DisposeStablePointer(child.pinned);
     __ DisposeStablePointer(impl1.pinned);