how to find Zero-boot packages with Hadrian?

[Norman Ramsey]

 > Norman Ramsey <nr at cs.tufts.edu> writes:
 > 
 > > What is the Hadrian equivalent of 
 > >
 > > make show VALUE=BOOT_PKGS
 > >
 > I don't believe there is currently a command-line equivalent. The list
 > itself is known as Settings.Default.stage0Packages.
 > 
 > What is your use-case?

I was updating the Commentary (commentary/libraries.md) and found this
text:

    To find out which packages are currently zero-boot packages, do
    the following in a GHC build:

    ```wiki
    $ make show VALUE=BOOT_PKGS
    ```

Since `make` will go away eventually, I wanted to tell people how to
discover zero-boot packages using Hadrian.


Norman