17.14 Respect both CC and CXX

The port should respect both CC and CXX variables. What we mean by this is that the port should not set the values of these variables absolutely, overriding existing values; instead, it should 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 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.