Use C99 printf statements in mingw

Otherwise, format specifiers such as %llu will not work on XP or
earlier.
This bug was introduced with 51ed9ec9.
http://sourceforge.net/apps/trac/mingw-w64/wiki/gnu%20printf
tests: add testcases for strprintf
Merge pull request #3244 from laanwj/2013_11_mingw_c99_printf

Use C99 printf statements in mingw