devel/creduce: switch to LLVM 13 branch and unbreak

The main upstream release of creduce requires LLVM 9 which we no longer
have in the ports tree. Fortunately, upstream provides branches with
compatibility to newer LLVM releases. Switch to the LLVM 13 branch and
update the port accordingly. The port version has been adjusted to
reflect this.

Approved by: bofh (maintainer)
MFH: 2023Q2