llvm/utils/valgrind/x86_64-pc-linux-gnu.supp: Add /usr/bin/cmp.
clang/utils/valgrind/x86_64-pc-linux-gnu_gcc-4.3.3.supp: Add /usr/bin/cmp.

FIXME: It could be removed if;

  - check-all included llvm/valgrind/supp, too.
  - clang-vg didn't use "check-all".