use PyDoc_STRVAR macro, so its possible to build without docstrings.

source/blender/python/generic/mathutils.c

@@ -38,9 +38,9 @@
 #include "BLI_math.h"
 #include "BLI_utildefines.h"
 
-static char M_Mathutils_doc[] =
+PyDoc_STRVAR(M_Mathutils_doc,
 "This module provides access to matrices, eulers, quaternions and vectors."
-;
+);
 static int mathutils_array_parse_fast(float *array, int array_min, int array_max, PyObject *value, const char *error_prefix)
 {
 	PyObject *value_fast= NULL;