Fix warnings about formats in printf-like functions on MS-Windows

Fix warnings about formats in printf-like functions on MS-Windows

* src/lisp.h (pI) [__MINGW32__]: Provide definition that will
hopefully DTRT with both MinGW64 and mingw.org's MinGW.  See
http://lists.gnu.org/archive/html/emacs-devel/2017-09/msg00171.html
for the details.
* src/conf_post.h (PRINTF_ARCHETYPE) [MINGW_W64]: Separate
definition specific to MinGW64.
(PRINTF_ARCHETYPE) [__MINGW32__]: For mingw.org's MinGW, use
__mingw_printf__ in ANSI-compatible mode.