gmath lib: avoid syntax error with __attribute__ in ctypes wrapping (trac https://trac.osgeo.org/grass/ticket/3331)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@71201 15284696-431f-4ddb-bdfa-cd5b030d7da7

include/gmath.h

@@ -24,6 +24,12 @@
 #define GRASS_GMATH_H
 
 #include <grass/config.h>
+
+#ifdef CTYPESGEN
+#undef __attribute__
+#define __attribute__(x)
+#endif
+
 #include <stddef.h>
 
 /*solver names */