add spec for building with a header file

spec/build_items/header.c

@@ -0,0 +1,7 @@
+#include <stdio.h>
+#include "header.h"
+
+int main(int argc, char *argv[])
+{
+    printf("The value is %d\n", VALUE);
+}

spec/build_items/header.h

@@ -0,0 +1,6 @@
+#ifndef HEADER_H
+#define HEADER_H
+
+#define VALUE 33
+
+#endif