rts: Don't keep findPtr symbol alive if not -DDEBUG
rts: Don't keep findPtr symbol alive if not -DDEBUG

Test Plan: Test with Hadrian

Reviewers: simonmar, snowleopard, erikd

Subscribers: rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4846

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc