Building gcc 3.1 with 64 bit support on Solaris 2.6?

[Adam Stein]

I can build a version of gcc 3.1 with 64 bit support if I'm compiling on Solaris 
8 (and running a 64 bit kernel).

What I would like to do is compile gcc 3.1 on a Solaris 2.6 running a 32 bit 
kernel (it is an ultrasparc machine if that matters).  In this way, gcc would be 
able to compile normally using 32 bit code which would run on Solaris 2.6 and 
up, but have the "-m64" option work when compiling on Solaris 8 systems without 
having two versions of gcc 3.1.

Is there any way to do this?  I've tried various combinations of configurations 
options, but it seems that gcc compiled on Solaris 2.6 won't have the "-m64" 
support when being run on Solaris 8 systems.

Any help is appreciated, even if you can tell me that you definitely can NOT do 
this.

Otherwise, I will have to have two versions of gcc, one for Solaris 2.6 and one 
for Solaris 8.

                                                Adam
--
Adam Stein @ Xerox Corporation       Email: adam@scan.mc.xerox.com
                                            
Disclaimer: All views expressed             
here have been proved to be my own.  [http://www.csh.rit.edu/~adam/]