First, make sure that
/usr/ccs/binare in your
$PATH(for the compiler, linker, and related tools).
Then you need this site.config.m4. The configuration that ships with Sendmail assumes that you're using gcc, with gcc's mechanism for generating dependencies. This just corrects that misconception.
That's enough to get Sendmail built.
% sh Build
doing the right thing. Tomorrow, with a bit of luck, I'll start adding DTrace instrumentation.