Add RAPIDCHECK_HEADERS to nix-shell environment

[YorikSar]

Motivation

Running ./configure in nix-shell environment currently ends up with this error:

checking for rapidcheck/gtest.h... no
configure: error: librapidcheck is not found.

There are workarounds in #7809, this change allows to run ./configure without them.

Context

See #7809 for more context.

Checklist for maintainers

Maintainers: tick if completed or explain if not relevant

• agreed on idea
• agreed on implementation strategy
• tests, as appropriate
  • functional tests - tests/**.sh
  • unit tests - src/*/tests
  • integration tests - tests/nixos/*
• documentation in the manual
• documentation in the internal API docs
• code and comments are self-explanatory
• commit message explains why the change was made
• new feature or incompatible change: updated release notes

Priorities

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[edolstra]

Strange, this works fine for me (in nix-shell and nix develop).

[roberth]

Configuring for rapidcheck is a recurring theme now.
This could settle it once and for all:

• Add pkg-config file? emil-e/rapidcheck#302

[Ericson2314]

The instructions are that one should run configurePhase, or perhaps ./configure $configureFlags. Plain running ./configure in the nix shell is not supported.

[Ericson2314]

@roberth is write the underlying issue is rapidcheck being odd. emil-e/rapidcheck#302 didn't get a response but @YorikSar if you would like to make a PR to fix that issue, we can apply it as a patch in Nixpkgs before it is merged.