SDK is incompatible with Xcode on Mojave

[n8jadams]

Upon running the following command (on macOS Mojave) from the build instructions

# From the $GOPATH/github.com/augustoroman/v8/v8/build/v8 directory...
gn gen out.gn/golib --args="is_official_build=true strip_debug_info=true v8_use_external_startup_data=false v8_enable_i18n_support=false v8_enable_gdbjit=false v8_static_library=true symbol_level=0 v8_experimental_extra_library_files=[] v8_extra_library_files=[]"

I get the following output:

********************************************************************************
 WARNING: The Mac OS X SDK is incompatible with the version of Xcode. To fix,
          either upgrade Xcode to the latest version or install the Mac OS X
          10.12 SDK. For more information, see https://crbug.com/620127.

 Current SDK Version:   10.14
 Current Xcode Version: 0100 (10A255)
********************************************************************************
ERROR at //build/config/mac/mac_sdk.gni:98:3: Assertion failed.
  assert(false, "SDK is incompatible with Xcode")
  ^-----
SDK is incompatible with Xcode
See //build/toolchain/mac/BUILD.gn:14:1: whence it was imported.
import("//build/config/mac/mac_sdk.gni")
^--------------------------------------
See //BUILD.gn:592:1: which caused the file to be included.
action("js2c") {
^---------------

Is there a workaround for this, where I can download the 10.12 SDK on my machine and use it for building? Thanks for the help.