Stubbed out the OS-specific files on macOS so I can actually start writing the uiControl tests.

darwin/control.m

@@ -0,0 +1,14 @@
+// 8 june 2019
+#import "uipriv_darwin.h"
+
+bool uiprivOSVtableValid(uiControlOSVtable *osVtable, const char *func)
+{
+	// TODO
+	return true;
+}
+
+uiControlOSVtable *uiprivCloneOSVtable(uiControlOSVtable *osVtable)
+{
+	// TODO
+	return NULL;
+}

darwin/meson.build

@@ -1,6 +1,7 @@
 # 23 march 2019
 
 libui_sources += [
+	'darwin/control.m',
 	'darwin/main.m',
 ]