When compiling SwiftShader, set BUILD_TESTS=OFF.

After https://swiftshader-review.googlesource.com/c/SwiftShader/+/19228,
SwiftShader fails to build without third_party/googletest unless
BUILD_TESTS is disabled.

Bug: skia:8054
Change-Id: If365fbbfc42dd3c41cc57be0fd7d494e7f83589d
Reviewed-on: https://skia-review.googlesource.com/133832
Reviewed-by: Ravi Mistry <rmistry@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Ben Wagner <benjaminwagner@google.com>
2 files changed