libc++ also defines these types for pre-C++11, and the two definitions
need to match to avoid redefinition errors.
Bug: 18300613
Change-Id: I1e9198d39f7c470f37bc6edba2dca2d499f54c9b
Split out all the UTF-8/16/32 handling code from String8/16 to its own
file to allow better reuse of code.
Change-Id: If9ce63920edc75472c38da4adce0d13cda9ad2f7