`rust` crashes when run without any arguments

[cypher]

I built rust from HEAD this morning (ac026e2), and when I run rust w/o any arguments, it produces the help output (although I'm not sure if it produces all of it?), then crashes with the following error:

rust(41022,0x10cfdd000) malloc: *** mmap(size=7522747388523884544) failed (error code=12)
*** error: can't allocate region
*** set a breakpoint in malloc_error_break to debug

I used Homebrew to compile rust, and I'm running Mac OS X 10.8.4. I've got the crash dump and other infos here: https://gist.github.com/cypher/7dc07c8e0461ab8c7daa

[huonw]

This appears to be a dup of #7617. (Reopen if you disagree.)