stdlib: Add assert() functions.

runtime/src/main/kotlin/kotlin/Assertions.kt

@@ -0,0 +1,20 @@
+package kotlin
+
+/**
+ * Throws an [AssertionError] if the [value] is false
+ * and runtime assertions have been enabled during compilation.
+ */
+public inline fun assert(value: Boolean) {
+    assert(value) { "Assertion failed" }
+}
+
+/**
+ * Throws an [AssertionError] calculated by [lazyMessage] if the [value] is false
+ * and runtime assertions have been enabled during compilation.
+ */
+public inline fun assert(value: Boolean, lazyMessage: () -> Any) {
+    if (!value) {
+        val message = lazyMessage()
+        throw AssertionError(message)
+    }
+}

runtime/src/main/kotlin/kotlin/Exceptions.kt

@@ -142,6 +142,9 @@ public class AssertionError : Error {
     constructor(message: String) : super(message) {
     }
 
+    constructor(message: Any) : super(message.toString()) {
+    }
+
     constructor(message: String, cause: Throwable) : super(message, cause) {
     }
 }