C2PY_xx macros are empty for gcc. Avoid warnings

Author: parcollet

src/c2py/user_api.hpp

@@ -6,11 +6,20 @@
 
 // -------------  Annotations for function ---------------
 
+// The attribute are only meaningfull for clang tools, hence for clang.
+#ifndef __GNUC__
 #define C2PY_IGNORE __attribute__((annotate("c2py_ignore")))
 #define C2PY_WRAP_AS_METHOD __attribute__((annotate("c2py_wrap_as_method")))
 #define C2PY_MODULE_INIT __attribute__((annotate("c2py_module_init")))
 #define C2PY_NOGIL __attribute__((annotate("c2py_nogil")))
 #define C2PY_RENAME(X) __attribute__((annotate("c2py_rename:" #X)))
+#else
+#define C2PY_IGNORE 
+#define C2PY_WRAP_AS_METHOD 
+#define C2PY_MODULE_INIT 
+#define C2PY_NOGIL 
+#define C2PY_RENAME(X) 
+#endif
 
 //#define C2PY_METHODS_AS_PROPERTY __attribute__((annotate("c2py_methods_as_property")))