Clang treats conversion of an unsigned constant to a signed one that
doesn't fit its range as an error. Make Visual Studio also produce an
error.

Change-Id: I2d392d5ba7765b72aa9e9478c5eee02102bdf286
Reviewed-on: https://swiftshader-review.googlesource.com/19648Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>