implement some stuff to make exaple SDL app run

NOTE: the main addition in this commit is WIP support for apps which
render on an EGL surface obtained using ANativeWindow_fromSurface

currently, this EGL surface is obtained by creating a 700x700 pixel
window with GLFW (the 700x700 size is hardcoded in several places)
and only Wayland is supported

ideally, we'd want to use a wayland subsurface to position the EGL
surface above the Surface widget it's associated with (and do
whatever for X11)

src/libandroid/looper.c

@@ -0,0 +1,22 @@
+#include <stddef.h>
+
+struct ALooper {
+	int dummy;
+};
+
+struct ALooper a_looper;
+
+struct ALooper* ALooper_forThread()
+{
+	return &a_looper;
+}
+
+struct ALooper* ALooper_prepare(int opts)
+{
+	return NULL;
+}
+
+int ALooper_pollAll(int timeoutMillis, int* outFd, int* outEvents, void** outData)
+{
+	return 0;
+}