Entry point selection.

$ kotlinc -entry foo.bar.qux ...

selects `qux(args: Array<String>):Unit` in the package `foo.bar` as an entry point.

The short flag is `-e`.

backend.native/tests/runtime/basic/libentry2.kt

@@ -0,0 +1,8 @@
+fun fail() {
+    println("Test failed, this is a wrong main() function.")
+}
+
+fun foo(args: Array<String>) {
+    println("Hello.")
+}
+