Support Clang and libc++ for Android build

[GoogleCodeExporter]

As of r439, Mozc for Android is using STLPort by default.  However, dependency 
on STLPort is a blocker to enable C++11 library features, e.g., Issue 242, 
which requires std::unique_ptr support.  We need to switch to up-to-date C++ 
STL library.

One possible solution would be switching to GNU libstdc++, but probably we may 
prefer libc++ with Clang, which is released under more permissive licenses (the 
MIT license and the UIUC License).

Original issue reported on code.google.com by yukawa@google.com on 13 Dec 2014 at 6:07

• Blocking: Deprecate base/scoped_ptr.h #219