Annotate LLNDK functions in non-vendor libraries

The ABI tool analyzes the source code of LLNDK libraries. It compiles
the source with the flags for core variants where __INTRODUCED_IN_LLNDK
does not version the API. To expose the version information to the ABI
tool, __INTRODUCED_IN_LLNDK is defined as an "annotate" attribute in
core variants.

Test: make
Bug: 314010764
Change-Id: I798a397f0e7567ca54db5e4aff4235933ebd3943