message: Use xz for cocoa artifacts
diff: @@ -460,8 +460,8 @@ def doBuildAppleDevice(String sdk, String buildType, String version) {
  mkdir -p install/lib
  cp src/realm/${buildType}/librealm.a install/lib
  cd install
  - tar -cvzf realm-core-${sdk}os-${version}-${buildType.toLowerCase()}.tar.gz lib include
  - mv *.tar.gz ..
  + tar -cvJf realm-core-${sdk}os-${version}-${buildType.toLowerCase()}.tar.xz lib include
  + mv *.tar.xz ..
  """
  } finally {
  collectCompilerWarnings('clang', true)
  