pkg/52833: devel/kbuild package needs to be updated to build VBoxGA.

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>Number:         52833
>Category:       pkg
>Synopsis:       devel/kbuild package needs to be updated to build VBoxGA.
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    pkg-manager
>State:          open
>Class:          change-request
>Submitter-Id:   net
>Arrival-Date:   Sun Dec 17 02:00:00 +0000 2017
>Originator:     ITOU (Sunagawa) Keiki
>Release:        NetBSD 8.99.8
>Organization:
individual
>Environment:
System: NetBSD atomic 8.99.8 NetBSD 8.99.8 (GENERIC) #0: Mon Dec 11 01:47:45 JST 2017 keiki@atomic:/usr/src/sys/arch/amd64/compile/obj/GENERIC amd64
Architecture: x86_64
Machine: amd64
>Description:
Updated devel/kbuild pkg to the latest SVN revision r3127 to build VirtualBox Guest Addtions 5.x under -current (this machine).

>How-To-Repeat:
attempt to use VirtualBox Guest Edditions for NetBSD/amd64 guest then
find that latest version of VirtualBox needs latest SVN revision of
kBuild to be built.

>Fix:
Here is the patch against current pkgsrc/devel/kbuild.
https://www.dropbox.com/s/kfvuzoltvy18tq9/kbuild.diff?dl=0

Since the SVN revision has no archive for distribution, we need to 
obtain the source tree with the svn checkout or export command from 
its SVN repository.

I don't know how to handle this case, so I make an archive from the
svn exported source tree and use it as a distfile.
Or should we specify svn to BUILD_DEPENDS and execute "svn export in
make extract stage?