chore: move __c_cpp/* to __ffi

__ffi/cpp/src/main.rs

@@ -0,0 +1,16 @@
+#[macro_use]
+extern crate cpp;
+
+cpp!{{
+    #include <stdio.h>
+    #include <iostream>
+}}
+
+fn main() {
+    unsafe {
+        cpp!([] {
+            printf("Hello, World!\n");
+            std::cout << "Hello, World2!" << std::endl;
+        });
+    }
+}