NEW: devel/creduce

Hi ports --

Attached is a new port, devel/creduce. C-Reduce is a C and C++ program
reducer.

---
pkg/DESCR:
C-Reduce is a tool that takes a large C, C++, or OpenCL file that has a
property of interest (such as triggering a compiler bug) and
automatically produces a much smaller C/C++ file that has the same
property. It is intended for use by people who discover and report bugs
in compilers and other tools that process source code.

C-Reduce is a fixpoint computation that calls a collection of plugins.
It is these plugins that actually transform the test case that is being
reduced. C-Reduce is thus very easy to improve and extend. Additionally,
the C-Reduce core can exploit multiple cores without exposing plugins to
concurrency.
---

Works well on amd64 following the user guide on the HOMEPAGE. Note that
this links libLLVM-6.0.so from devel/llvm, though that does not get
reflected in WANTLIB (I left a comment saying such in the Makefile).

OK?

~Brian