Problem when compiling with -j4 on Solaris (only!)

[Hubert Feyrer <hubert%feyrer.de@localhost>]

When building the netbsd-5 branch with -j4 on Solaris (only!), I get build 
errors like the following:

        ...
        --- dependall-libXi ---
        /usr/homes/feyrer/cvs/src-5/obj.i386/tooldir/bin/i386--netbsdelf-ranlib 
libXi_pic.a
===> nbmake: nbmake: don't know how to make 
/usr/homes/feyrer/cvs/src-5/obj.i386/usr/homes/feyrer/cvs/src-5/external/mit/xorg/lib/libXext/libXext.so.
        Stop
        *** [dependall] Error code 2

I've tried to build without -j, and things work there. Is there some place 
in src/external/mit/xorg where parallel builds may be a problem? And if 
so, why would that only show up when building on Solaris, while it works 
fine on NetBSD, Linux, Mac OS? How can I debug this?

Thanks!


 - Hubert