Fix transitive whole_static_libs on prebuilt static libraries

whole_static_libs on static library usually uses the .o files from
the dependency, but on a prebuilt static library has to use the .a file.
whole_static_libs on a static library that itself has whole_static_libs
on a prebuilt static library also needs to use the .a file transitively.

Test: TestWholeStaticLibPrebuilts
Change-Id: I9d4aabf72be0941b461a72e610f2b28287251cb2