How do I circumvent the use of clang during build?

[Chris H]

Greetings,
 I recently made a <failed> attempt to move from RELENG_8
to RELENG_9. I've been on BSD since the early 80's, and with
the exception of a couple of failed kernels (my fault), I've
never had one failure with the build(world|kernel) ||
install(world|kernel). The only notable difference I noticed,
was the addition of clang. While I can't (yet) conclusively
blame it on clang. I _can_ say, that the whole process took _3_
times longer, than without. So my question is; is it possible
to build(world|kernel) && install(world|kernel) without the
clang toolchain? If for no other reason but to discover whether
clang was responsible for the failure, and whether building w/o
clang is any faster.

Thank you for all your time, and consideration.

--Chris