DECserver build fails with gummy structure

["Tim Leonard, Cantab." <leonard@ricks.enet.dec.com>]

I'm trying to build AKCL on a DECstation, and I run into a problem I don't know
what to do about.

The machine is actually a DECserver 5500 with 160 MB of memory, running Ultrix
4.2.  Datasize limit is 256 MB, stack limit is 2 MB.  The C compiler is DEC c89
for RISC.

I get the kcl and akcl (version 1-600) tar files, and unpack them according to
instructions, taking care to preserve dates.  The MACHINES file lists a dec3100,
which should be close enough to a DECserver 5500 (they're both MIPS RISC
machines).  I edit akcl/h/dec3100.defs to define the MAINDIR path.  I add_defs
dec3100.  I make -f Smakefile, it runs for a long time (spewing mounds of
warnings about illegal structure pointers), and then it bombs, with:
	.
	.
	.
	ccom: Warning: ../c/iteration.c, line 124: illegal structure pointer 
	combination
	        result =        (arg)->c.c_cdr->c.c_car->c.c_cdr;
	      --------------------------------------------------^
	(ccom): ../c/iteration.c, line 159: ccom: Internal: gummy structure
	                                eval(   (result)->c.c_car);
	      --------------------------------------------^
	*** Error code 1

	Stop.

Have I done something foolish, I hope?

Tim