CLabel: Catch #11155 during C-- pretty-printing
CLabel: Catch #11155 during C-- pretty-printing

In #11555 we ended up generating references to the non-existence
stg_ap_0_upd. Here we add asserts to verify that we don't generate
references to non-existent selector or application symbols.

It would likely also make sense to add further asserts during code
generation, so we can catch the issue even closer to its source.

Test Plan: Validate

Reviewers: simonmar, austin, ezyang

Reviewed By: simonmar, austin

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2230

GHC Trac Issues: #11155

ezyang/ghc,shlevy/ghc,shlevy/ghc,sdiehl/ghc,sgillespie/ghc,sdiehl/ghc,vTurbine/ghc,sgillespie/ghc,olsner/ghc,olsner/ghc,snoyberg/ghc,vikraman/ghc,vTurbine/ghc,sgillespie/ghc,sgillespie/ghc,ezyang/ghc,sdiehl/ghc,shlevy/ghc,ezyang/ghc,mettekou/ghc,vikraman/ghc,vTurbine/ghc,vikraman/ghc,sdiehl/ghc,olsner/ghc,vTurbine/ghc,sdiehl/ghc,mettekou/ghc,ezyang/ghc,snoyberg/ghc,mettekou/ghc,vTurbine/ghc,sdiehl/ghc,vTurbine/ghc,snoyberg/ghc,ezyang/ghc,olsner/ghc,mettekou/ghc,mettekou/ghc,sdiehl/ghc,snoyberg/ghc,vTurbine/ghc,shlevy/ghc,olsner/ghc,snoyberg/ghc,olsner/ghc,vikraman/ghc,vikraman/ghc,mettekou/ghc,shlevy/ghc,ezyang/ghc,snoyberg/ghc,sgillespie/ghc,shlevy/ghc,ezyang/ghc,vikraman/ghc,mettekou/ghc,shlevy/ghc,snoyberg/ghc,vikraman/ghc,sgillespie/ghc,sgillespie/ghc,olsner/ghc