Remove the vestigial llndk_library and replace it with properties
in the llndk clause of the implementation cc_library.
In order to reduce duplication of the arch-specific headers used
by the implementation and LLNDK, rename libc_headers_arch to
libc_llndk_headers and hoist the "include" directory out of it,
since that directory is preproccessed separately for LLNDK
libraries.
Bug: 170784825
Test: m checkbuild
Test: compare out/soong/build.ninja
Change-Id: I75f0ff9129d910640da55eee6a6387467e6e4a9d
a0a4a6c296