Fix CMake Subzero build.
Fix CMake Subzero build.

Bug swiftshader:116

Change-Id: I93208ea733cfe69474477ad2e00e52c8e86d1e25
Reviewed-on: https://swiftshader-review.googlesource.com/c/21268
Tested-by: Nicolas Capens <51edc787c30f24c4904e8ffbb5523c3a9f7a451d@google.com>
Reviewed-by: Alexis Hétu <1c7141772178a7e80858c3db5052b328076f08f4@google.com>

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