Use real snprintf when available.
Use real snprintf when available.

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/10688
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader