COMP: Do not warn about unused typedefs.

GCC 4.8 adds a warning about local unused typedefs, but making sure these types
are available is an important part of the ITK ConceptChecking framework.
Disable the check with a compiler flag.

Change-Id: I59040e9d445822d0ba9a0b846fe7f11e58bc76d3
Merge branch 'release'

Change-Id: If358084c1b498643c4211d17cd1073b543011516