userland: add assembly support

Move arm assembly cheat here, and start some work on x86 cheat as well.

userland/arch/main.c

@@ -0,0 +1,17 @@
+/* This is the main entrypoint for all .S examples. */
+
+#include "stdio.h"
+#include "stdint.h"
+
+#include "lkmc.h"
+
+int asm_main(uint32_t *line);
+
+int main(void) {
+    uint32_t ret, line;
+    ret = asm_main(&line);
+    if (ret) {
+        printf("error %d at line %d\n", ret, line);
+    }
+    return ret;
+}