updating /usr/include

["James K. Lowden" <jklowden%schemamania.org@localhost>]

$ uname -srm
NetBSD 5.0.2 amd64
http://mail-index.netbsd.org/pkgsrc-bugs/2010/05/06/msg037897.html
http://mail-index.NetBSD.org/source-changes/2009/11/15/msg003245.html

What is the right way to update /usr/include if I want to stick with
5.0?  

I want to build dxr (https://github.com/mozilla/dxr).  To do so I need
only and exactly clang 3.0. On first attempt to build it I hit the
problems Jeremy reported that Christos had fixed 6 months prior, all
this nearly two years ago.  Apparently wchar_t was being defined for C+
+.  (I don't know if that was something NetBSD added or GNU left in.)  

I'm not eager to perturb my build environment.  I've been down the road
of updating gcc in pkgsrc and overriding CFLAGS etc. and I've had more
fun at the dentist.  I'm especially reluctant because I'd be upgrading
GCC only to get clang to experiment with dxr.  

But you tell me.  Can I safely update /usr/include and /usr/lib, or
should I either update the OS or use pkgsrc?  

--jkl