SpirvShader: Implement SMod.
SpirvShader: Implement SMod.

Test: *smod*
Bug: b/126873455
Change-Id: If946e72d23aa9386b85cffe96b02ab63195f0a24
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/26549
Tested-by: Ben Clayton <1f693eb7158dc33015048c09d6712f74dabddf79@google.com>
Reviewed-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>

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