pragma Pure_12 [(library_unit_NAME)];
This pragma is only available in GNAT mode (-gnatg switch set)
and is intended for use in the standard run-time library only. It has
no effect in Ada 83, Ada 95, or Ada 2005 modes, but is
pragma Pure when operating in later
Ada versions. This is used to handle some cases where packages
not previously pure became so in Ada 2012.