re2c: enable parallel building, enable tests
re2c: enable parallel building, enable tests

Parallel builds speed up building considerably.
Tests don't add much of an overhead.

Signed-off-by: Sergei Trofimovich <110fdadc76b6bce16977f568bdb4723eaed6fb3f@gentoo.org>

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs