third_party/clspv: Add GN build files The clspv project uses CMake for build. Adding support for GN build in here. The build is currently setup to generate linux/x86 and android/arm64 artifacts for now and relevant gn files are placed in `third_party/clspv` location. Bug: angleproject:8369 Change-Id: Iec7ef1916617a8b8a93324ff7302f89bd571b814 Signed-off-by: Gowtham Tammana <g.tammana@samsung.com> Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5106594 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>