armeabi support was removed from the Android NDK so we should no
longer build it. Since this fixes the Android build failures this
commit also re-enables Travis Android builds.
While re-enabling Android builds, some recent changes broke C++98
support so this fixes those issues as well which include:
- Conditionally compiling use of move constructors, operators and
std::move.
- Changing sample to use flatbuffers::unique_ptr rather than
std::unique_ptr.
Finally, added the special "default_ptr_type" value for the
"cpp_ptr_type" attribute. This expands to the value passed to
the "--cpp-ptr-type" argument of flatc.
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