Sounds like a CPU bug then. Recompiling made it so that certain instruction (or sequence of instructions) are not hit - avoiding hitting some kind of hardware problem. But the problem is still there.
What makes me think it may be CPU rather than GCC is that the segfault seems to happen nondeterministicly in a single-threaded bash binary running the same shell script with the same arguments each time.
Somebody also reported this oddity:
Strangely enough, the machine can run mprime for days on end without any trouble. However, an average run of the Glasgow Haskell Compiler's testsuite exhibits a handful of failures (typically segmentation faults). Even stranger, if I run a few mprime threads alongside a run of GHC's testsuite, mprime will itself sometimes crash with a segmentation fault.
So you have the same mprime binary which either crashes or not depending on whether GHC tests are running at the same time.