`Unrecognized field 'cpp-options'` in cabal.project

[sjakobi]

Describe the bug
cabal-install doesn't seem to recognize the cpp-options I have configured in my cabal.project.

To Reproduce
Steps to reproduce the behavior:

1. Checkout unordered-containers at haskell-unordered-containers/unordered-containers@c481228

2. Add the following cabal.project

packages: .

package unordered-containers
  cpp-options: -DBENCH_containers_Map

$ cabal build
Warning: /home/simon/src/unordered-containers/cabal.project: Unrecognized
field 'cpp-options' on line 4

Expected behavior
The CPP options are recognized and applied.

System information

$ cabal --version
cabal-install version 3.6.2.0
compiled using version 3.6.2.0 of the Cabal library 
$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 8.10.7