Error building with Xcode 9.1, because "system" call has been removed

Should affect Xcode 9.X generally. The error occurs on line 88 of `src/frontend/iosclient.cc` (`int unused __attribute((unused)) = system( "locale" );`).

A quick workaround is to just comment out the line -- its apparent purpose is to output locale information to the user, in case the locale is not UTF-8 native.

I was able to build and run the blink shell successfully under iOS 11.2.2 after making the above change, but I have not tested the mosh functionality yet (ssh works fine).

Keep up the great work on this awesome project! :-)

Start at line 88 of src/frontend/iosclient.cc and inspect the system("locale") call that fails with Xcode 9.1. Build the blink shell under an affected Xcode 9.x/iOS environment, then verify the shell and mosh functionality still work without the build error.

Written by the indexing model from the issue text.