message: Add a temporary requirement for Mac bots to have XCode.
diff: @@ -124,11 +124,15 @@ buckets {
  name: "mac-dbg"
  dimensions: "os:Mac-10.13"
  mixins: "debug"
  + # Require XCode temporarily to avoid https://crbug.com/884015
  + dimensions: "xcode_version:9.3"
  }
  builders {
  name: "mac-rel"
  dimensions: "os:Mac-10.13"
  mixins: "release"
  + # Require XCode temporarily to avoid https://crbug.com/884015
  + dimensions: "xcode_version:9.3"
  }
  # Linux: test combinations of {clang,msvc}x{release,debug}x{x86,x64}
  @@ -250,12 +254,16 @@ buckets: {
  name: "mac-dbg"
  dimensions: "os:Mac-10.13"
  mixins: "debug"
  + # Require XCode temporarily to avoid https://crbug.com/884015
  + dimensions: "xcode_version:9.3"
  }
  # Actually on the CQ
  builders {
  name: "mac-rel"
  dimensions: "os:Mac-10.13"
  mixins: "release"
  + # Require XCode temporarily to avoid https://crbug.com/884015
  + dimensions: "xcode_version:9.3"
  }
  # Actually on the CQ
  