clang build of libc on netbsd-6 fails

[Jan Danielsson <jan.m.danielsson%gmail.com@localhost>]

Hello,

   Sync'd earlier today, and building yields:

   /usr/src/lib/libc/thread-stub/thread-stub.c:415:1: error: function
'__libc_thr_exit_stub' could be declared with attribute
      'noreturn' [-Werror,-Wmissing-noreturn]

   Adding "__dead" attribute/macro to function makes clang happy.

-- 
Kind regards,
Jan Danielsson