Make single-file classes tolerant to having many main()'s

compiler/testData/codegen/boxMultiFile/mainInFiles/1.kt

@@ -0,0 +1,21 @@
+package test
+
+class A {}
+
+fun getMain(className: String): java.lang.reflect.Method {
+    val classLoader = A().javaClass.classLoader
+    return classLoader.loadClass(className).getDeclaredMethod("main", Array<String>::class.java)
+}
+
+fun box(): String {
+    val bMain = getMain("pkg.AKt")
+    val cMain = getMain("pkg.BKt")
+
+    val args = Array(1, { "" })
+
+    bMain.invoke(null, args)
+    cMain.invoke(null, args)
+
+    return args[0]
+}
+

compiler/testData/codegen/boxMultiFile/mainInFiles/a.kt

@@ -0,0 +1,5 @@
+package pkg
+
+fun main(args: Array<String>) {
+    args[0] += "O"
+}

compiler/testData/codegen/boxMultiFile/mainInFiles/b.kt

@@ -0,0 +1,5 @@
+package pkg
+
+fun main(args: Array<String>) {
+    args[0] += "K"
+}