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-cfi.c

@@ -25,9 +25,9 @@
 /* This must come before any other includes.  */
 #include "defs.h"
 
-#include <math.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <math.h>
 #include <stdbool.h>
 #include <unistd.h>
 #ifdef HAVE_SYS_MMAN_H