The change does not impact the product mode.

In non product mode, CodeStrings allows to associate a linked list of strings to a CodeBuffer, CodeBlob or Stub. In addition, with ASSERTS, it defines a boolean asserting whether the list of strings are valid.

Here are the issues addressed by this CR:

- The old code mentioned the fact that CodeStrings was not always correctly initialized. This will be addressed by the fix, allowing check_valid to be added at a few locations where it could currently failed due to uninitialized values.

- As a minor extension, it will be possible for platform dependent code to modify the comment separator used by print_block_comment, which was hard coded to " ;; ".

- As another minor extension of the validity assertion, freeing a code string will not necessarily mark it (and hence its Stub/CodeBlob/CodeBuffer) as invalid. If CodeStrings contains only comment, removing them does not change the validity of the CodeStrings.