Avoid a problem in libc_freeres() seen on a linux-i686 buildbot when running

under valgrind:

==19577== Invalid free() / delete / delete[]
==19577==    at 0x4C9C866: free (vg_replace_malloc.c:325)
==19577==    by 0x5121104: ??? (in /lib/libc-2.10.2.so)
==19577==    by 0x4C97412: _vgnU_freeres (vg_preloaded.c:62)
==19577==    by 0x5041486: __run_exit_handlers (exit.c:93)
==19577==    by 0x50414FE: exit (exit.c:100)
==19577==    by 0x5028B5C: (below main) (libc-start.c:254)
==19577==  Address 0xffffffff is not stack'd, malloc'd or (recently) free'd
==19577== 

Apparently this happens under certain versions of glibc, so valgrind provides
the --run-libc-freeres=no option to avoid calling freeres().  This may increase
the number of "still reachable" blocks valgrind reports, but we don't care
about those, while this error breaks the buildbots.

There are upstream bugs about this at
http://sourceware.org/bugzilla/show_bug.cgi?id=10610 and
http://bugs.kde.org/show_bug.cgi?id=167483, but they don't look likely to be
fixed.

llvm-svn: 98813