I've been attempting to use Windows with Cygwin to compile NetBSD.  I wanted 
to "seed" the inevitable Google search our customers will be doing when they 
attempt the same with NetBSD on our products by offering some tidbits of 
information.  The current information google returns is a bit out-dated.

*) The top-level "build.sh" shell script in the NetBSD source distribution 
needs a small modification on cygwin because cygwin's /bin/pwd does not 
support -P:

--- build.sh.orig       2006-06-16 10:00:25.812500000 -0700
+++ build.sh    2006-06-16 10:05:13.468750000 -0700
@@ -89,6 +89,12 @@
        unset PWD
        TOP=$(/bin/pwd -P 2>/dev/null)

+       # Some systems do not support the -P option to /bin/pwd
+       #
+       if [ -z "$TOP" ]; then
+               TOP=$(/bin/pwd 2>/dev/null)
+       fi
+
        # Set defaults.
        #
        toolprefix=nb

*) I'd recommend normalizing your PATH while in cygwin to /bin:/usr/bin e.g. 
export PATH=/bin:/usr/bin  I had some programs in my path that happened to 
conflict with some of the tools used in the build.

*) Make sure you get the "minires-devel" package from Cygwin or else you 
will get a tools build failure in asn1_compile.   That build will be looking 
for the "resolv.h" and "nameser.h" include files that come with that package 
and I don't think that package is selected by default when installing 
cygwin.

*) The current Cygwin distribution as of 6/16/2006 has a problem with the 
cygwin /usr/include/sys/stdio.h-- It includes an unconditional declaration 
of getline().  This has been fixed in the current Cygwin CVS for many 
months, but hasn't made it to a release yet.  You can do the modification 
yourself to this file:

--- stdio.h.orig        2006-06-16 10:31:46.187500000 -0700
+++ stdio.h     2006-06-16 09:51:16.421875000 -0700
@@ -28,8 +28,10 @@

 __BEGIN_DECLS

+#ifdef _GNU_SOURCE
 ssize_t        _EXFUN(getline, (char **, size_t *, FILE *));
 ssize_t        _EXFUN(getdelim, (char **, size_t *, int, FILE *));
+#endif /* _GNU_SOURCE */

 __END_DECLS

*) Due to the nature of the Windows filesystem you can't e.g. have both a 
'CVS' dir and a 'cvs' executable in the same directory.  This will cause 
build problems
when traversing the cleandir rule of cvs where it tried to "rm -f *.o blah 
blah cvs".  The build will fail with "Can't remove cvs -- is a directory"  I 
fixed this by just recursively removing the 'CVS' directories in the source 
dist-- you don't really need them unless you want to track future CVS 
changes.  You can do that with this command from the top-level directory: 
find . -type d -name 'CVS' | xargs rm -rf

With the above worked around, I was successfully able to build the cross 
tools and also use ./build.sh to compile a kernel for evbarm (./build.sh -m 
evbarm kernel=TS7200)  I haven't attempted to make release yet so there may 
be some more unknown issues there.

//Jesse Off