[Nix-dev] php-packages fix (broken since multiple outputs)

[Marc Weber]

Problem: Since outputs = ["out" "dev"] a lot of php-packages stopped
compiling because php-config provided wrong includes

http://mawercer.de/tmp/php-packages-out-dev.patch
  - moves php-config into php.dev
  - patches the includes directory so that headers are found
  - The patch also rewrites the assertion so that I could test all
    packages easily by 

      nix-build  -A php71Packages


My question is, is there a different way to run nix-build  -A php71Packages
ignoring assertions so that all php packages can be tested easily?

I'd like to prepare a PR.

Marc Weber