Build of head fails in unsafeLookupUnit

Summary

Hadrian build of master branch at commit 2e63a0fb fails with

Steps to reproduce

Building master on x86_64 terminates with:

...
| Run Ghc LinkHs Stage1: ../ghc-build/master/stage1/utils/hp2ps/build/c/AreaBelow.dyn_o (and 17 more) => ../ghc-build/master/stage1/bin/hp2ps
ghc: panic! (the 'impossible' happened)
  (GHC version 9.1.0.20201111:
        unsafeLookupUnit
  rts   
  Call stack:
      CallStack (from HasCallStack):
        callStackDoc, called at compiler/GHC/Utils/Panic.hs:181:37 in ghc:GHC.Utils.Panic
        pprPanic, called at compiler/GHC/Unit/State.hs:519:17 in ghc:GHC.Unit.State

Please report this as a GHC bug:  https://www.haskell.org/ghc/reportabug

Error when running Shake build system:
  at action, called at src/Rules.hs:40:19 in main:Rules
  at need, called at src/Rules.hs:62:5 in main:Rules
* Depends on: ../ghc-build/master/stage1/bin/hp2ps
  at cmd', called at src/Builder.hs:312:23 in main:Builder
  at cmd, called at src/Builder.hs:408:8 in main:Builder
* Raised the exception:
Development.Shake.cmd, system command failed
Command line: ../ghc-build/master/stage0/bin/ghc -Wall -hisuf dyn_hi -osuf dyn_o -hcsuf dyn_hc -fPIC -dynamic -hide-all-packages -no-user-package-db '-package-db ../ghc-build/master/stage1/lib/package.conf.d' -i -i/home/viktor/dev/ghc/../ghc-build/master/stage1/utils/hp2ps/build -i/home/viktor/dev/ghc/../ghc-build/master/stage1/utils/hp2ps/build/hp2ps/autogen -i/home/viktor/dev/ghc/utils/hp2ps -Iincludes -I../ghc-build/master/stage1/lib -I../ghc-build/master/stage1/utils/hp2ps/build -I/usr/include -I../ghc-build/master/stage1/lib -optc-I../ghc-build/master/stage1/lib -optP-include -optP../ghc-build/master/stage1/utils/hp2ps/build/hp2ps/autogen/cabal_macros.h -outputdir ../ghc-build/master/stage1/utils/hp2ps/build -dynamic -optl-Wl,-rpath,$ORIGIN/../lib/x86_64-linux-ghc-9.1.0.20201111 -optl-Wl,-rpath,$ORIGIN/../../../lib/x86_64-linux-ghc-9.1.0.20201111 -optl-Wl,-zorigin -no-auto-link-packages -no-hs-main -lm -Wnoncanonical-monad-instances -optc-Wno-error=inline -optP-Wno-nonportable-include-path ../ghc-build/master/stage1/utils/hp2ps/build/c/AreaBelow.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Curves.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Error.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Main.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Reorder.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/TopTwenty.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/AuxFile.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Deviation.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/HpFile.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Marks.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Scale.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/TraceElement.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Axes.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Dimensions.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Key.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/PsFile.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Shade.dyn_o ../ghc-build/master/stage1/utils/hp2ps/build/c/Utilities.dyn_o -o ../ghc-build/master/stage1/bin/hp2ps -O2 -H32m -XHaskell2010 -no-global-package-db -package-db=/home/viktor/dev/ghc/../ghc-build/master/stage1/lib/package.conf.d -ghcversion-file=/home/viktor/dev/ghc/../ghc-build/master/stage1/lib/ghcversion.h

Expected behavior

Successful build

Environment

• GHC version used: 8.10 while compiling master

Optional:

• Operating System: Fedora 31
• System Architecture: x86_64