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/os_ios.go

@@ -252,6 +252,4 @@ func createWindow(win *Window, opts *WindowOptions) error {
 }
 
 func Main() {
-	// iOS runs in c-archive mode, so this is never reached.
-	panic("call to Main from outside main")
 }