Pull in libmedia's exported headers in libbtif

Do this by listing libmedia as a shared library linked by libbtif.
We won't actually be able to link against libmedia because static
libraries don't work like that, but surrounding logic about headers
is triggered.

Bug: 27804373
Test: libbtif compiles in the presence of a new exported header path
      in libmedia.

Change-Id: Ic1e776966daaf70b7b9ae6ea99af89bc9a0b3885