HPCC-9431 Allow constant folder to resolve functions in eclrtl

If the extension is missing from the library name, then prefix it with the
default library prefix as well as adding the default filename extension.

(This mirrors the behaviour in LoadSharedObject)

Signed-off-by: Gavin Halliday <gavin.halliday@lexisnexis.com>
Merge pull request #4468 from ghalliday/issue9431

HPCC-9431 Allow constant folder to resolve functions in eclrtl

Reviewed-By: Richard Chapman <rchapman@hpccsystems.com>