The port should respect both CC and CXX variables. If it does not, please add NO_PACKAGE=ignores either cc or cxx to the Makefile.
An example of a Makefile respecting both CC and CXX variables follows. Note the ?=:
CC ?= gcc
CXX ?= g++
Here is an example which respects neither CC nor CXX variables:
CC = gcc
CXX = g++
Both CC and CFLAGS variables can be defined on FreeBSD systems in /etc/make.conf. The first example defines a value if it was not previously set in /etc/make.conf, preserving any system-wide definitions. The second example clobbers anything previously defined.