Visual C++ 2015 provides an actual snprintf implementation, so we
shouldn't use _snprintf, which does not guarantee null-termination.

Bug swiftshader:75

Change-Id: Ia45e49e77a6076e8f9f12ad74c6ad50dbdbf2dbd
Reviewed-on: https://swiftshader-review.googlesource.com/10688Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>