Obsolete +BUILD_INFO keys

[Jonathan Perkin <jperkin%pkgsrc.org@localhost>]

Does anyone legitimately use the following fields in +BUILD_INFO?

  BUILD_HOST
  CC_VERSION
  GMAKE
  PERL

While looking at cleaning up the PROVIDES/REQUIRES handling I noticed 
these that have been there since around 1998 and I don't think they 
provide any useful information, nor see why they are special (i.e. if 
we're logging these then why not hundreds of other tools?)

If nothing else they're wasting a bunch of execs for every package, and 
making an already very complicated target even more so, and so I'd like 
to remove them.

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