Just a clarification on the discovery history:
"found when building Steel Bank Common Lisp (SBCL) using the new compiler" is not exactly
correct. The problem was found when building SBCL, which doesn't use gcc, but which does use
libc6. There was a change in Debian unstable that introduced a new version of libc6 2.7-8 ->
2.7-9. That new version was compiled with gcc 4.3.0. When SBCL builds with this version of
libc6, it either hangs or spins the CPU at 100%.