4.0.2 RC2 Solaris 10 x86: configure, x86-64, and atomicity.h

[Andrew Morrow]

On a Solaris 10 Opteron machine, I can let configure guess the target
as i386-pc-solaris2.10, and bootstrap works fine. I get a very nice
multilib install that can generate x86-64 targets. However, libstdc++
ends up with a poor version of bits/atomicity.h, specifically
libstdc++/config/cpu/i386/atomicity.h. That implementation uses a
mutex to simulate atomic integers. For performance reasons I need
libstdc++ to use the config/cpu/i486/atomicity.h that uses the "lock"
mnemonic.

If I try to configure with i[456]86-pc-solaris2.10, bootstrap fails
when compiling 64 bit targets, and informs me that the CPU I have
selected does not support the x86-64 instruction set. If I try to
configure with arguments like opteron-pc-solaris2.10,
x86-64-pc-solaris2.10, amd64-pc-solaris2.10, etc., these fail to
configure at all.

Is there configure target that will let libstdc++ choose the better
implementation for atomicity.h and also succeed when building the 64
bit targets?

Thanks