New BUILDINFO variable

[Alan Barrett <apb%netbsd.org@localhost>]

I have just committed some changes to allow information from the 
build environment to be stored in /etc/release and in kernels.

You can store information about your build in the BUILDINFO 
environment variable, to pass it to build.sh via -V 
BUILDINFO="Your information here".  The value may be a multi-line 
string, with embedded C-style escapes, so line breaks may be 
denoted by \n or by literal line breaks (or a mixture of both).

The BUILDINFO value will appear near the top of /etc/release if 
you build a release, and will be stored in the kernel's buildinfo 
variable if you build a kernel.  The value bay be extracted from a 
running kernel via sysctl kern.buildinfo.

For example, if you pass something like this to build.sh:

   BUILDINFO='Built from my private git repository
   branch foo, commit deadc0ffee, date 2014-08-03,
   based on NetBSD-current as of 2014-08-03 10:00 UTC'

then sysctl kern.buildinfo would print that information, 
and information like this would appear near the top of 
${DESTDIR}/etc/release:

Build information:
         Build date   Sun Aug  3 22:47:03 UTC 2014
           Built by   user@host.domain

       Built from my private git repository
       branch foo, commit deadc0ffee, date 2014-08-03,
       based on NetBSD-current as of 2014-08-03 10:00 UTC


--apb (Alan Barrett)