Replace use of deprecated C Standard library headers in C++ code.

Change-Id: I9fa6630c7e4bdb2897df34d417635d8c7d8253bc
Signed-off-by: Tyler Chatow <tchatow@gmail.com>
diff --git a/build_tests/helloworld.cc b/build_tests/helloworld.cc
index c034e96..f12349e 100644
--- a/build_tests/helloworld.cc
+++ b/build_tests/helloworld.cc
@@ -1,5 +1,3 @@
-#include <stdio.h>
+#include <cstdio>
 
-int main() {
-  printf("Hello, World!\n");
-}
+int main() { printf("Hello, World!\n"); }