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

[dje at gcc dot gnu.org]

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

--- Comment #9 from David Edelsohn <dje at gcc dot gnu.org> ---
I would have expected _XOPEN_SOURCE=500 to be defined in a host-specific
configure file (like libstdc++-v3/config/os/.../os_defines.h) or added to the
compile line in configure.