printf: cast variables to the expected type

%x expects unsigned int and %p expects void *

GCC emits a diagnostic about %p/void* in pedantic mode:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=26542
use MRB_STRINGIZE

It's defined in mruby/version.h which gets included in mruby.h, so it's
safe to use.
remove unused MSVC strtoll fallback
Merge pull request #2564 from cremno/use-mrb_stringize

use MRB_STRINGIZE
Merge pull request #2563 from cremno/printf-cast-variables-to-expected-type

printf: cast variables to the expected type
Merge pull request #2565 from cremno/remove-unused-msvc-strtoll-fallback

remove unused MSVC strtoll fallback