add [static|shared].apex_available to cc_library

apex_available property can be appended differently per the linkage
type. This will be used to restrict certain libs (e.g.
libc_malloc_debug) to an APEX while allowing them to be statically
linkable from platform for testing purpose.

Test: m (apex_test amended)
Change-Id: I6dec23129c5ac93a3ef06fea28f26f240c0ba410