Don't #define snprintf in VS 2015 or higher.

In VS 2015 and higher snprintf is supplied and therefore vsnprintf
doesn't need to be defined. This also avoids problems caused by
_snprintf being different from snprintf.

This fixes a build break with VS 2015 and improves security.

R=tomfinegan@chromium.org
BUG=440500

Review URL: https://codereview.chromium.org/1055603003
1 file changed