Make libc2dcolorconvert 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 libc2dcolorconvert with BOARD_VNDK_VERSION=current
Bug: 69526027
Change-Id: I7d7aeec7851b47ea1d4fa71f0271a364a13edef9