[ntcore] Add ntcoreffi binary (#4471)

Co-authored-by: Peter Johnson <johnson.peter@gmail.com>

ntcoreffi/src/main/native/c/ntcoreffi.c

@@ -0,0 +1,11 @@
+// Copyright (c) FIRST and other WPILib contributors.
+// Open Source Software; you can modify and/or share it under the terms of
+// the WPILib BSD license file in the root directory of this project.
+
+#define AddFunctionToLink(FuncName) \
+  extern void FuncName(void);       \
+  FuncName()
+
+void DoNotCallMeImOnlyForLinking(void) {
+#include "ExportedSymbols.h"
+}