Add LLNDK support for the VNDK

Instead of using the NDK headers and libraries, add LL-NDK specific
headers and library stubs for VNDK users. This allows us to provide an
expanded liblog interface.

Test: aosp_arm; m -j
Test: Enable BOARD_VNDK_VERSION on aosp_arm; m -j
Change-Id: I0197f44c91218c73b9567a05320c91a2baaae39b