manually roll swiftshader

some of the cmake flags changed names

c.f. https://swiftshader.googlesource.com/SwiftShader.git/+/f6d3cbb2830306f3ef51a72cd3f798684d107c14

Change-Id: I6f5f7d06c88035c097d7079ef93665110d15be70
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/264291
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
4 files changed