libiberty: fix build of gdb with clang

This use a upstream fix at
https://gcc.gnu.org/ml/gcc-patches/2008-07/msg00292.html

BUG=475970
TEST=CC=x86_64-cros-linux-gnu-clang CXX=x86_64-cros-linux-gnu-clang++
     emerge-falco gdb

Change-Id: Ia46631625ad600adfe314ad6e36c154a10cfad4a
1 file changed