ghci can't run :main

Summary

ghci fails with *** Exception: expectJust getLinkDeps if you invoke :main <file> from the repl (or ghcid)

Steps to reproduce

• new ghc repo
• in hadrian/ghci.sh, replace build.cabal.sh with build.stack.sh (I couldn't get cabal to run)
• add --run=":main testsuite/tests/typecheck/should_compile/DfltProb1.hs" to .ghcid (on a new line)
• hadrian/ghci.sh --configure once for configuration
• ghcid

Expected behavior

Compile file testsuite/tests/typecheck/should_compile/DfltProb1.hs

Actual behavior

*** Exception: expectJust getLinkDeps
CallStack (from HasCallStack):
  error, called at compiler/utils/Maybes.hs:55:27 in ghc:Maybes
  expectJust, called at compiler/ghci/Linker.hs:719:28 in ghc:Linker

Environment

• GHC version used: 8.6.5 to compile master (b0fdd7fe)

Optional:

• Operating System: Linux
• System Architecture: 64bit