Make libbt-vendor build with the VNDK.

When the vndk is enabled (BOARD_VNDK_VERSION=current),
vendor libraries must only link against vendor variants
in the build system. This also means that they receive
restricted sets of headers and that automatic global
headers are restricted.

Test: build libbt-vendor with BOARD_VNDK_VERSION=current
Bug: 69526027
Change-Id: I2ff78cccc417d0fff8cacb8b82fa8dc3d6f074ab
7 files changed