libapt-pkg-perl fails to cross build from source for two distinct
reasons. The versioned build dependency on perl requests a host
architecture Perl interpreter. That ends up conflicting with the base
system. Annotating it :native is needed here to get a runnable one.

The upstream build system overrides the CC variable with a C++ compiler.
The build infrastructure normally populates it with a cross compiler,
but the override prevents that. I suggest enhancing the overriding
mechanism.

You may find both changes in the attached patch. Once applying it,
libapt-pkg-perl cross builds successfully.

Helmut