[Bug other/63758] liblto_plugin.so has undefined reference to _environ on OSX

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63758

--- Comment #8 from Iain Sandoe <iains at gcc dot gnu.org> ---
posted as
https://gcc.gnu.org/ml/gcc-patches/2015-09/msg00447.html
with Eric's suggested move of environ.h -> include/
checked with a bootstrap on darwin12 that libiberty.a only contains references
to _NSGetEnviron().