What's the problem this feature will solve?

Prevent builds from running when all required build dependencies are not present.

Describe the solution you'd like

pip fails to build with a descriptive message when a build dependency is missing, providing a nicer user experience (IMHO).

Alternative Solutions

1. Use python-build which does exactly that.
2. Manually parse pyproject.toml + generate egg info, get additional build requires and validate those are in the environment.

Additional context
I see the pip docs on --no-build-isolation state "Build dependencies specified by PEP 518 must be already installed if this option is used.". I was wondering whether pip would like to mimic the behaviour that python-build has on --no-isolation(Fail nicely if build dependencies are not present) and if so I'm happy to try and push a patch.

Related: #6718