Silence a pedantic GCC warning by adding reinterpret_cast<void*>.

Here we're casting a function pointer to `void*`, which is not doable
with our implicit-conversions-only `hr::voidp(x)` helper, and is
not even doable with a `static_cast`; we must `reinterpret_cast`.

glhr.cpp

@@ -625,7 +625,7 @@ void init() {
         printf("Failed to initialize GLEW\n");
         return;
         }
-      printf("CreateProgram = %p\n", __glewCreateProgram);
+      printf("CreateProgram = %p\n", reinterpret_cast<void*>(__glewCreateProgram));
       if(!__glewCreateProgram) noshaders = true;
       }
   #endif