Confusion about how to specify and also override ( gcc vs clang and versions)

[Jeffrey Bouquet]

I wonder if anyone knows a page where one can be sure the lines in one's make

conf are correct, and also a command line to override the setting.
For instance

CC=/usr/local/bin/clang33
CXX+= ...
As, how many of those are supposed to exist?
Are the more for some compilers than others?
Other things to consider within the make.conf?
The way they should be written for each of gcc46, gcc47, clang, clang33

And a way to override whatever is in make conf, as...
make CLANG=/usr/local/bin/clang33 build  ...  is supposed to work?  Or 
some other suggested or proven method?

Checking wiki.freebsd.org I don't see any specific page.
Searching for the information in the forums has for a short time not yielded much informaiton.

I've six of seven distinct make.conf's (make.conf.clang, make.conf.aria2c, ...) that I'd like
to standardize the syntax of the compiler within all of. 

Thanks if anyone knows.

J. Bouquet