Allow calling v?dprintf for any target API level.

Old versions of Android called these fdprintf and vfdprintf out of
fears that the glibc names would collide with user debug printfs.

Allow users to just use dprintf and vfdprintf on any version by
renaming those calls to their legacy equivalents if needed.

Test: built trivial NDK module targeting android-14 and using dprintf
Test: make checkbuild
Bug: https://github.com/android-ndk/ndk/issues/72
Change-Id: I90de149278f931380418536abaef47c5cee5c195