Turns out that $PATH was pointing to a cc wrapper with
a bunch of warning flags set for LP64 porting.  Turned that
off and it works.

Now I get:

cc  -O2 -Werror -Wall -Wstrict-prototypes -Wmissing-prototypes  -Wpointer-arith -Wno-main -mno-fp-regs -I. -I../../../../arch -I../../../.. -nostdinc -DDIAGNOSTIC -DDEBUG -DLKM -DMAXUSERS=32 -D_KERNEL -Dalpha  -c ../../../../ufs/lfs/lfs_alloc.c
cc1: warnings being treated as errors
../../../../ufs/lfs/lfs_alloc.c: In function `lfs_vfree':
../../../../ufs/lfs/lfs_alloc.c:355: warning: int format, different type arg (arg 3)
*** Error code 1

Stop.

I commented out lfs (not using it anyway) and it built.

Thanks to Aaron J. Grier and Ross Harvey for their replies.

-Snoopy