Build failure on latest master

[Michael Sanders]

Seeing the following build error when running the bootstrap script on master:

Configure SwiftySwiftVim..
SSVIM CMAKE START
Building boost
-- Boost version: 1.67.0
-- Found the following Boost libraries:
--   coroutine
--   context
--   filesystem
--   program_options
--   system
--   thread
--   chrono
--   date_time
--   atomic
Attempting to find system SourceKit
Using Sourcekit from Xcode install at: /Applications/Xcode.app/Contents/Developer.
SSVIM CMAKE FINISH
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/mks/.icmd/third_party/swiftyswiftvim/build
Build SwiftySwiftVim..
[  8%] Building CXX object CMakeFiles/integration_tests.dir/APIIntegrationTests.cpp.o
/Users/mks/.icmd/third_party/swiftyswiftvim/APIIntegrationTests.cpp:1:9: fatal error: 'arpa/inet.h' file not found
#import <arpa/inet.h>
        ^~~~~~~~~~~~~
1 error generated.
make[2]: *** [CMakeFiles/integration_tests.dir/APIIntegrationTests.cpp.o] Error 1
make[1]: *** [CMakeFiles/integration_tests.dir/all] Error 2
make: *** [all] Error 2

[I] ~/.i/t/swiftyswiftvim ((47b34e87…)|✔) $ xcodebuild -version
Xcode 10.2.1
Build version 10E1001

Any ideas?