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Previously, the struct name and its typedef name were identical.  This
confuses emacs and etags.  This change eliminates the typedef names and
removes the extern "C" wrapping the libdex header files.  To support
this change the transitive C dependencies have been made to compile as
C++ instead.

Change-Id: I7065f32d61d776f9b09c7b461adf2502268d852f