checksum argmax fix #2

[Jonathan Perkin <jperkin%mnx.io@localhost>]

I've tidied up my previous patch a little, and figured it'd be best to 
start a new thread.  To make it easier for folks to review and test I've 
pushed it here:

  https://github.com/TritonDataCenter/pkgsrc/commit/3c561ed25e0df2cf8407e4d83bc7369f4ccb7b2a

As always just append .patch or .diff to the URL if you want to grab a 
raw copy, or checkout the dev/distinfo-argmax branch via git.

I've removed any mktool bits to simplify things, and changed some of the 
variables to names that I'm happier with.  Packages now set e.g.
DISTINFO_ARGMAX_REQD=524288 to enable the check.

This seems to do the right thing in various tests across both NetBSD and 
macOS, with and without native make, as well as testing with e.g.  
TOOLS_PLATFORM.mktemp= to ensure it's correctly pulled in as a bootstrap 
dependency, but I'd be much happier with more widespread testing.

Thanks,

--
Jonathan Perkin   -   mnx.io   -   pkgsrc.smartos.org
Open Source Complete Cloud   www.tritondatacenter.com