[R] X11 installation problem Linux X86_64

[Robert Nelson]

Hello all,

This is my first time posting, so forgive my ignorance.  I've searched high 
and low but haven't come across the specific answer to my questions.

configure runs fine, then make gives this error:

...
gcc -shared -L/usr/local/lib -o R_X11.so  dataentry.lo devX11.lo rotated.lo 
rbitmap.lo   -L/usr/X11R6/lib -lX11  -ljpeg -lpng -lz  -lreadline -ldl 
-lncurses -lm
/usr/bin/ld: skipping incompatible /usr/X11R6/lib/libX11.so when searching 
for -lX11
/usr/bin/ld: skipping incompatible /usr/X11R6/lib/libX11.a when searching 
for -lX11
/usr/bin/ld: cannot find -lX11
collect2: ld returned 1 exit status
make[4]: *** [R_X11.so] Error 1
make[4]: Leaving directory `/root/R-2.0.1/src/modules/X11'
...

This is a 64-bit machine, so I'm wondering if the problem stems from make 
not looking in the /usr/X11R6/lib64 directory, as opposed to 
/usr/X11R6/lib64.  Both dirs are in /etc/ld.so.conf.  I also tried 
configure --x-libraries=/usr/X11R6/lib64, but that produced the same 
error.  I believe that I have all the requisite packages installed.  Could 
someone please point me in the right direction?  Thanks in advance

-Robert