Update xdmf to compile with clang 3.4 and c++11 enabled.

Change-Id: Ie9b337d48b26fe4a67700c0dbbff55827cd9739c
Merge topic 'clang_libc++11_support' into master

873da3e4 Update xdmf to compile with clang 3.4 and c++11 enabled.