sim: reorder header includes

We're including system headers after local headers in a bunch of
places, but this leads to conflicts when our local headers happen
to define symbols that show up in the system headers.

Use the more standard order of:
* config.h (via defs.h)
* system headers
* local library headers (e.g. bfd & libiberty)
* sim specific headers

sim/common/dv-glue.c

@@ -22,10 +22,10 @@
 /* This must come before any other includes.  */
 #include "defs.h"
 
-#include "hw-main.h"
-
 #include <string.h>
 
+#include "hw-main.h"
+
 /* DEVICE