[chore] Use gnu-efi as a part of project

efi/lib/exit.c

@@ -0,0 +1,19 @@
+#include "lib.h"
+
+VOID
+Exit(
+    IN EFI_STATUS   ExitStatus,
+    IN UINTN        ExitDataSize,
+    IN CHAR16       *ExitData OPTIONAL
+    )
+{
+    uefi_call_wrapper(BS->Exit,
+            4,
+            LibImageHandle,
+            ExitStatus,
+            ExitDataSize,
+            ExitData);
+
+    // Uh oh, Exit() returned?!
+    for (;;) { }
+}