If USE_X11 is defined pkgsrc/mk/buildlink3/bsd.buildlink3.mk replaces
X11BASE with BUILDLINK_X11_DIR (which is
${BUILDLINK_DIR:H}/.x11-buildlink) in include and library paths.

In my case LOCALBASE is /usr/local/pkg/lib and X11BASE is /usr. The
include and library paths originally contain LOCALBASE, but the /usr
gets replaced by BUILDLINK_X11_DIR.
As a result, the compiler tries to include
work/..x11-buildlink/local/pkg/..., which does not exist. Therefore
certain header files are not found, for example. (happens for example
for libwww's header files).
What is the rationale behind using X11BASE as a replacement pattern
rather than LOCALBASE? Wouldn't that require that packages such as
libwww are installed under X11BASE rather than LOCALBASE?
Or is it a problem that the paths first have X11BASE replaced, after
which in my case LOCALBASE no longer matches since the X11BASE string is
contained in the LOCALBASE string?   
  
-- 
Georg Schwarz    http://home.pages.de/~schwarz/
 geos@epost.de     +49 177 8811442