MK_CLANG_IS_CC mis-formed when compiling ports

[Thomas D. Dean]

I built FrfeeBSD 9 with
WITHOUT_CLANG="Yes"

When I try to build the net/bwn-firmware-kmod/

I get an error that MK_CLANG_IS_CC is mis-formed.

If I define this in make.conf, I get an error that the user may not set 
this.

If I use 'make MK_CLANG_IS_CC="no"' the port compiles.

How do I fix this?

Tom Dean