win32: fix %zu fixups - dont use mingw's vsnprintf

win32: fix %zu fixups - dont use mingw's vsnprintf

Traditionally, MSVCRT has provided vsnprintf as _vsnprintf;
to 'aid' portability/standards compliance, mingw provide a
static version of [v]snprintf that is buggy.

The bug manifests as %lx is treated as a 64bit argument not
32bit, ie consumes two 32bit parameters.  if a %s were to
follow a %lx, bad things can happen.

Solution: Be sure to use the MSVCRT version, at least it
behaves as expected

Additionally, make it a bit more obvious when vlc wrappers
are being called by other wrappers.

Signed-off-by: David Flynn <davidf@rd.bbc.co.uk>
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>