This was broken by D3746 and/or D3809, but unfortunately we didn't
notice because CI at the time wasn't building the profiling way.

Test Plan:
```
cd testsuite/test/profiling/should_run
make WAY=ghci-ext-prof
```

Reviewers: bgamari, michalt, hvr, erikd

Subscribers: rwbarton, thomie, carter

GHC Trac Issues: #14705

Differential Revision: https://phabricator.haskell.org/D4437

(cherry picked from commit 488d63d6)