fix issue #1804 (warning about redefined macros)

Author: wjakob

include/pybind11/pybind11.h

@@ -41,16 +41,15 @@
 #  endif
 #endif
 
-#if defined(__GNUG__) && !defined(__clang__)
- #include <cxxabi.h>
-#endif
-
-
 #include "attr.h"
 #include "options.h"
 #include "detail/class.h"
 #include "detail/init.h"
 
+#if defined(__GNUG__) && !defined(__clang__)
+#  include <cxxabi.h>
+#endif
+
 NAMESPACE_BEGIN(PYBIND11_NAMESPACE)
 
 /// Wraps an arbitrary C++ function/method/lambda function/.. into a callable Python object