Much like the C front-end, ensure that the collection of objects of
static lifetime is initialised in a fixed order, based on their names.
Previously, the (unspecified) order in an unordered set and unordered
map determined the sequence of instructions being generated, which
resulted in jdiff regression tests sometimes failing. Those failures
were caused by __CPROVER_initialize sometimes showing up among the list
of goto functions that differed.

The functional change is the second commit, the first just does the refactoring to make the second commit as small (and as easy to review) as possible.

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.