how to enable -m64 on x86-linux for building ATLAS

["Dennis Wassel" <dennis.wassel@googlemail.com>]

Hi,

I've been trying to compile the ATLAS library on an 32-bit Linux
system with my self-compiled gcc 4.3.0, but this fails.
It boils down to the ATLAS config utility noticing that I have a
64-bit processor and trying to compile some low-level stuff with -m64,
which doesn't work because I have not compiled in 64-bit support. [I
could force 32-bit mode, but I feel that 64-bit mode surely improves
performance, which is what ATLAS is for in the first place]

Ok, so I try and recompile gcc, telling it that I do indeed have a
64-bit processor, and it "profiledbootstrap"s itself merrily, until at
some point ld whines that it cannot find a compatible libc.

Fine. I'm now going to try to build a 64-bit glibc (and worry where to
put it later, because I'm not root), and possible the full-fledged
binutils toolchain and so on, but now I feel this
chicken-and-egg-problem creeping up to me - wouldn't I need 64-bit
support in my compiler to create the corresponding glibc?

D'oh!

Any pointers, docs or howtos anyone? Much appreciated!

Cheers,
Dennis