shared: add _nm_pure/_nm_const define for __attribute__ ((pure))/((const))

shared/nm-macros-internal.h

@@ -28,6 +28,8 @@
 
 #define _nm_packed __attribute__ ((packed))
 #define _nm_unused __attribute__ ((unused))
+#define _nm_pure   __attribute__ ((pure))
+#define _nm_const  __attribute__ ((const))
 
 #define nm_auto(fcn) __attribute__ ((cleanup(fcn)))