core/lib: compiler_hints guard NORETURN and PURE
core/lib: compiler_hints guard NORETURN and PURE

kaspar030/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT,RIOT-OS/RIOT