improving bootstrapping of WITH_CLANG_IS_CC

[Warner Losh]

On Sep 10, 2012, at 4:56 PM, Brooks Davis wrote:
> .if ${COMPILER_TYPE} != "clang"
> 
> I'd like to commit this in the next few days unless there are objections
> requiring a major redesign.

Due to other $LIFE happening, I just scanned the patch, but I really like it.

I'd also propose a COMPILER_VERSION variable be reserved so that can be set so that variations in compiler versions can be comprehended in the tree to allow easier external toolchain support as well.  I have no impl for this yet, but just thought I'd put a bug in people's ear.

Warner