[FIX][Attributor] Fix broken build due to missing virtual deconstructors.

The lack some virtual deconstructors where causing some builds bots to fail.
This patch fixes that.

Problematic commit:
https://reviews.llvm.org/rGeaf1b6810ce0f40008b2b1d902750eafa3e198d3

Build bot:
https://lab.llvm.org/buildbot/#/builders/18/builds/1741