Sort mutually-recursive constants by linkage name, not id

[lukemaurer]

Since flexpect does a straightforward one-to-one comparison, the order
in which the bindings occur is important even within a recursive group,
and we can't have that order depend on something fragile like what
integer ids things happen to be assigned. Specifically, we get a
spurious test failure from a generated .flt test if the ids in the
original run happen to be different from the ids in the test run.
If we sort them by linkage name instead, the ordering should be
consistent.

[mshinwell]

Two comments:

1. Please add a signature on CIS_by_name.
2. We need some way of using the default CIS when not running through flexpect for performance. Maybe instantiate the SCC functor twice then use a first-class module to choose?