[Bug libobjc/63765] [5.0 Regression] libobjc testsuite failures on AIX caused by setting _XOPEN_SOURCE

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63765

--- Comment #10 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Let's go with the one defining _XOPEN_SOURCE only for Solaris until someone
programs David's suggestion of the host-specific configure file.