Really, this is an extrac complexity with no advantage (did we ever
use it?)  If users really want a small system they can choose the NONE
implementation of pp_printf.  The extra half a kilobyte saved by diag-no
is really not worth the effort:

% make clean; make -s ARCH=bare-i386 CONFIG_PRINTF_NONE=y
% size ppsi.o
   text    data     bss     dec     hex filename
  10323     208     264   10795    2a2b ppsi.o

% make clean; make -s ARCH=bare-i386 CONFIG_PRINTF_NONE=y PPSI_NO_DIAG=y
% size ppsi.o
   text    data     bss     dec     hex filename
   9792     208     264   10264    2818 ppsi.o
Signed-off-by: Alessandro Rubini <rubini@gnudd.com>