[ns] ns makefile question - reg X11 libs

[Sita S. Krishnakumar]

Hello,
I am building ns-2.27 on a 64 bit machine. When the ./install compiles and
links Tcl/Tk, it looks for X11 libs in /usr/X11R6/lib.
I would instead like for it to look at a different directory for 64 bit
libs. Where in the install or configure files in ns-2 should the change be
made such that it will get propagated into all the makefiles in the many
subdirectories?
Thanks for your help.
Regards,
Sita