FS-6500: freetdm: Add more enum compliance by defining proper enum values for FTDM_END and FTDM_ANY special state values

This library is used only by mod_enum and is available on most
platforms.  The version in our tree has many code quality problems
that are generating noise when doing static analysis.  Suffice it to
say we want rid of it as our responsibility.

FS-353

Since the first branch doesn't need to do anything, we invert it and
pull a sub-branch out a level into the main conditional.

...now this code needs refactoring.

We goto done at the end of these blocks.

This assignment isn't doing anything, so it safe to remove it, but
there remains the question of whether there could have been some
actually necessary intention behind this line.

execv(3) only returns on error, and will always return -1 in that
case.

Fix a use after free in a 'theoretical' case in switch_cache_db_persistant_execute_trans_full where the pre_trans_execute statement fails, but SQLSetAutoCommitAttr succeeds