An issue regrading %zu vasprintf NOT being recognized
by mingw runtime's 3.14 is fixed with an upgrade to 3.15
So make this the least required standart.
Note that this issue lead to a vlc early crash on windows
and is generally toxic on cases where %s is following a
misinterpreted %zu
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>