thrift: Fixed php binding install path

Not satisfied with the fix for #15937 - I've added a solution that does not require one to execute shell commands before brewing. Also the new superenv breaks the formular since thrift executes [php-config via backticks](https://github.com/apache/thrift/blob/master/lib/php/Makefile.am#L33) which ignores the configured path for php-config. The fix for this is to switch to the userpath env, so the homebrewed php can be used instead of the system php. 

If you can improve on the formular please do so, I can't figure out how to make it prettier, but I think this pull request is significant improvement over the status quo which is somewhat unhelpful caveats.