ui/app: call main from Android and iOS

Android can only run c-shared libraries which means that every
Gio program must create its window and event loop from an init
function.

The same applies to iOS but for a more benign reason: the gio tool
builds programs in c-archive mode for iOS and links the binary with
a Objective-C driver.

Allow Gio programs to run off its main function by linking to and
invoking main even from Android libraries and iOS ditto.

Signed-off-by: Elias Naur <mail@eliasnaur.com>

ui/app/runmain_ios.go

@@ -0,0 +1,10 @@
+// +build darwin,ios
+
+package app
+
+import "C"
+
+//export gio_runMain
+func gio_runMain() {
+	runMain()
+}