Improve D mixed language test case

test cases/d/10 d cpp/cppmain.cpp

@@ -1,6 +1,18 @@
+extern "C" int rt_init();
+extern "C" int rt_term();
 extern void print_hello(int i);
 
 int main(int, char**) {
+    // initialize D runtime
+    if (!rt_init())
+        return 1;
+    
     print_hello(1);
+    
+    // terminate D runtime, each initialize call
+    // must be paired with a terminate call.
+    if (!rt_term())
+        return 1;
+    
     return 0;
 }

test cases/d/10 d cpp/libfile.d

@@ -1,5 +1,5 @@
-import core.stdc.stdio;
+import std.stdio;
 
 extern (C++) void print_hello(int i) {
-    printf("Hello. Here is a number printed with D: %d\n", i);
+    writefln("Hello. Here is a number printed with D: %d", i);
 }