Building NetBSD without gcc

[Daniel Loffgren <miyokojiro%gmail.com@localhost>]

I have been working on getting NetBSD to compile without gcc, and was making 
good progress on 5.1, but decided to move over to current. However, when 
setting CC in a (for example, the kernel) makefile in current, it just gets 
ignored and gcc gets used regardless. I noticed that /usr/share/mk/bsd.own.mk 
now has some TOOL_CC variables for various compilers, and found some mention of 
it on the mailing lists, but how is this meant to be used? Should variables 
like CC be completely thrown out by the user? What if they want to use a 
compiler that isn't on this TOOL_CC list?