Add basic VNDK support in Make

Add BOARD_VNDK_VERSION and LOCAL_USE_VNDK to specify the version of the
VNDK that will be used globally, and whether to use the VNDK on a module
basis.

If the board is using the VNDK:

* LOCAL_COPY_HEADERS may only be used by modules defining LOCAL_USE_VNDK
* LOCAL_USE_VNDK modules will compile against the NDK headers and stub
  libraries, but continue to use the platform libc++.
* LOCAL_USE_VNDK modules will not have the global includes like
  system/core/include, but it will use device-specific kernel headers.

This change does not attempt to enforce any linking constraints, that
will come in a later patch.

Test: out/build-aosp_arm.ninja is identical before/after
Change-Id: Icce65d4974f085093d500b5b2516983788fe2905