py: Move to guarded includes, everywhere in py/ core.
Addresses issue #1022.
diff --git a/py/modmath.c b/py/modmath.c
index b922f3e..38ed390 100644
--- a/py/modmath.c
+++ b/py/modmath.c
@@ -24,16 +24,12 @@
* THE SOFTWARE.
*/
-#include <math.h>
-
-#include "mpconfig.h"
-#include "misc.h"
-#include "qstr.h"
-#include "obj.h"
-#include "builtin.h"
+#include "py/builtin.h"
#if MICROPY_PY_BUILTINS_FLOAT && MICROPY_PY_MATH
+#include <math.h>
+
/// \module math - mathematical functions
///
/// The `math` module provides some basic mathematical funtions for