9.2.1-alpha1 can't bootstrap? Data.Binary.FloatCast: Can't be safely imported

I compiled the source tarball (ghc-9.2.0.20210331-src.tar.xz) with ghc-8.10.4 (./configure --prefix=... && make -j) and installed the result.

Then I wanted to compile the source again, with ghc-9.2.0.20210331 (just built) in the PATH. This quickly fails with

[ 13 of 299] Compiling Data.Binary.Put  ( libraries/binary/src/Data/Binary/Put.hs, bootstrapping/Data/Binary/Put.o )

libraries/binary/src/Data/Binary/Put.hs:103:1: error:
    Data.Binary.FloatCast: Can't be safely imported!
    The module itself isn't safe.
    |
103 | import Data.Binary.FloatCast (floatToWord, doubleToWord)
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
utils/genprimopcode/ghc.mk:19: utils/genprimopcode/dist/package-data.mk: No such file or directory
make[1]: *** [utils/ghc-cabal/ghc.mk:59: utils/ghc-cabal/dist/build/tmp/ghc-cabal] Error 1
make: *** [Makefile:124: all] Error 2