OpenSC used SUSv3 "z" printf length modifier for printing size_t variables,
however this modifier is not available on Windows ("I" must be used
instead), at least for now.
Introduce SC_FORMAT_LEN_SIZE_T define for that purpose and convert existing
code to use it when printing size_t variables.
This define can't go into libopensc/internal.h since tools use it, too.
Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>