A warning treated as an error was causing the
official build to fail. Added -Wno-unused-result
to the LLVM build file to solve the issue.

Also ran 'git cl format' on the BUILD.gn files
to fix all formatting issues.

Change-Id: I235c7d9d3e60f788e1dc694a40991c214e6c77e3
Reviewed-on: https://swiftshader-review.googlesource.com/8110Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>