The port must respect both CC and CXX variables. What we mean by this is that the port must not set the values of these variables absolutely, overriding existing values; instead, it may append whatever values it needs to the existing values. This is so that build options that affect all ports can be set globally.
If the port does not respect these variables, 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 CXX 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.