http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49745
--- Comment #13 from Jakub Jelinek <jakub at gcc dot gnu.org> 2011-07-14 21:54:36 UTC --- I think only libstdc++ installs the gthr* headers, all other uses inside of gcc just include it in library *.c files rather than headers, so for _LIBOBJC it IMHO shouldn't be harmful if unistd.h is included.
