configure: Make compilable with VS2015

So Visual Studio 2015 has some breaking changes regarding the C
runtime. In short, they made C99 compatable runtime.
Refer to http://blogs.msdn.com/b/vcblog/archive/2014/06/18/crt-features-fixes-and-breaking-changes-in-visual-studio-14-ctp1.aspx



Made-Seriously-Happy: "Ronald S. Bultje" <rsbultje@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>