[Bug other/49661] et-forest.h uses extern "C"

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49661

--- Comment #3 from joseph at codesourcery dot com <joseph at codesourcery dot 
com> ---
libiberty is a C library.  I don't consider that relevant to any code not 
actually part of libiberty.