Allow Android font manager on *nix.

There is nothing left in the SkFontMgr_android.cpp which is specific
to Android, so allow it to be built and used on *nix platforms. This
allows for easier development and testing.

The only reason to limit to *nix platforms are the dependencies on
Expat and FreeType. This should be buildable and runnable on other
platforms when these dependencies are also available.

Review URL: https://codereview.chromium.org/1228833003
2 files changed