Looking at http://gcc.gnu.org/gcc-4.3/changes.html, this is the only
thing that really jumps out:
"GCC no longer places the cld instruction before string operations.
Both i386 and x86-64 ABI documents mandate the direction flag to be
clear at the entry of a function. It is now invalid to set the flag in
asm statement without reseting it afterward."
...but (1) SBCL _should_ be resetting the direction flag before any
calls to libc code, and (2) I would expect problems caused by this to
be more deterministic.