Makes overrideAttrs usable in the same way that `override` can be used.
It allows the first argument of `overrideAttrs` to be either a function
or an attrset, instead of only a function:
hello.overrideAttrs (old: { postBuild = "echo hello"; })
hello.overrideAttrs { postBuild = "echo hello"; }
Previously only the first example was possible.
Co-authored-by: adisbladis <adisbladis@gmail.com>
Co-authored-by: matthewcroughan <matt@croughan.sh>
