Stop umount.cifs from building on non-merged builds

[Tim Prouty]

Hi Jelmer/Metze,

I can't seem to figure out how to stop umount.cifs from building  
during the "make test" portion of a merged build.  Not all systems  
have the headers/libs required to build [u]mount.cifs. The source3  
configure correctly determines that it can't be built and rightfully  
skips building it, but something during the merged build is causing it  
to still get built (and fail).  You can see the problem happening on  
this build machine:

http://build.samba.org/?function=View+Build;host=isilon-samba;tree=samba_3_master;compiler=gcc;revision=1247051722

I have spent some serious time staring at the source4 build scripts,  
but I haven't really gotten any leads. Can either of you help point me  
in the right direction?

Thanks!

-Tim