[FR] use libandroid_support for all pre-21 builds?

[DanAlbert]

libandroid_support is currently coupled to libc++, but the headers are used unconditionally. This means that decls for things in libandroid_support are always present, so in the rare cases where libc++ isn't used (C only, or C++ builds that explicitly don't use the stdlib), using the functions that are provided by libandroid_support leads to degraded diagnostics (an undefined reference when linking instead of a "that API was added in $API_LEVEL" message).

Since the headers are there anyway, it might be good to always use libandroid_support rather than only when libc++ is used. It'd let us clean up a lot and reduce C vs C++ behavior differences.

[DanAlbert]

No such thing any more. No longer needed.