[xml] use mingw C99 compatible functions {v}snprintf instead those from MSVC runtime

[Roumen Petrov <bugtrack roumenpetrov info>]

Hi All,

Please could you review and test enhancement from attachment 
"0001-use-mingw-C99-compatible-functions-v-snprintf-instea.patch".
It is registered as request 
https://bugzilla.gnome.org/show_bug.cgi?id=676427 .

Since version 3.15 mingw runtime implement C99 compatible *printf 
functions in particular {v}snprintf.
The difference is visible in libxslt regression test if environment 
variable PRINTF_EXPONENT_DIGITS is set to 2 - regression tests pass.

Regards,
Roumen

Attachment: 0001-use-mingw-C99-compatible-functions-v-snprintf-instea.patch
Description: Text Data