MFH: r531918

comms/openzwave-devel: fix build on GCC architectures

Use C++11 compiler:
cc1plus: error: unrecognized command line option "-std=c++11"

Adding MAKE_ARGS+= CXX="${CXX}" is necessary because CXX is set up in Makefile.

Approved by: portmgr (fix build blanket)