Ensure that in and out are only defined once.

I'm not actually certain that the #include guard is necessary,
but it doesn't hurt.

Author: jmct

langs/evildoer/main.c

@@ -3,6 +3,9 @@
 #include "types.h"
 #include "runtime.h"
 
+FILE* in;
+FILE* out;
+
 void print_result(int64_t);
 void print_char(int64_t);
 

langs/evildoer/runtime.h

@@ -1,3 +1,6 @@
+#ifndef RUNTIME_H
+#define RUNTIME_H
 int64_t entry();
-FILE* in;
-FILE* out;
+extern FILE* in;
+extern FILE* out;
+#endif /* RUNTIME_H */