win32: don't assume the format specifier for the stdlib printf/scanf like functions
When using the mingw printf shims for C99 compat the msvc format specifiers don't work and the build fails.
Ideally we would use glib functions which abstract this away, but in the error handler context we shouldn't call back into glib. And for scanf we don't have a glib wrapper.
Instead call the "secure" versions provided by the win32 API (_snprintf_s/fprintf_s/sscanf_s) which mingw doesn't replace.
Edited by Christoph Reiter