64 Bit build for Sparc

Hi
I was reading the Postgres solaris installation instructions in the hope
of finding some hints on how to compile postgres for 64 bit.

I installed the gcc3.1 and the 3.1 libraries found on the
sunfreeware.com site and tried to compile postgres 7.2.1 by setting the
CFLAG to -m64.

At onepoint  the build failed with the following error message. "file
fe-auth.o wrong ELF class ELFCLASS64"

Now I was wondering  if...
A: Is it possible to compile postgres with gcc for 64 bit , and what is
required
B: if there any indication that this will improve performance
C: there are any known problems with 64 bit builds of postgres on solaris

Any help, instruction, comments  would be greatly appreciated.
I try to build the server on a SunFire 280R

Kind regards
Alex