Implement vector sign mask operations.
Implement vector sign mask operations.

Bug swiftshader:15

Change-Id: I0d9cb2daeea931994abeb63f0939879875d4e81f
Reviewed-on: https://swiftshader-review.googlesource.com/7791
Reviewed-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>
Tested-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>
Reviewed-on: https://swiftshader-review.googlesource.com/8148
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

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