`cabal new-build` failed with "ghc-pkg: 1: Parse of field 'name' failed"

I'm trying to install 'cabal/Cabal' from git, and getting this:

```
>> cabal new-build exe:cabal
In order, the following will be built (use -v for more details):
cabal-install-2.1.0.0
Preprocessing executable 'cabal' for cabal-install-2.1.0.0..
Building executable 'cabal' for cabal-install-2.1.0.0..
Generating manual page
/Users/m/git/cabal/dist-newstyle/build/cabal-install-2.1.0.0/build/cabal/cabal.1
...
Package contains no library to register: cabal-install-2.1.0.0...
cabal: '/usr/local/bin/ghc-pkg' exited with an error:
ghc-pkg: 1: Parse of field 'name' failed.
```