Forget about using an OpenBSD host to cross-build.  Apparently the toolchain is 
incompatible (see assembly errors).  One cannot even build tools target:

#   compile  compat/md2hl.lo
cc -O  -I. -I./include -I/fsimages/usr/src/tools/compat 
-DHAVE_NBTOOL_CONFIG_H=1  -D_FILE_OFFSET                _BITS=64 
-D__DBINTERFACE_PRIVATE -c -o md2hl.lo.o 
/fsimages/usr/src/tools/compat/../../lib/li bc/hash/md2/md2hl.c
In file included from /fsimages/usr/src/lib/libc/hash/md2/md2hl.c:17:
/fsimages/usr/src/lib/libc/hash/hashhl.c:36: error: syntax error before "asm"
In file included from /usr/include/sys/_types.h:37,
                  from /usr/include/sys/types.h:44,
                  from /fsimages/usr/src/tools/compat/compat_defs.h:32,
                  from nbtool_config.h:526,
                  from /fsimages/usr/src/tools/compat/namespace.h:9,
                  from /fsimages/usr/src/lib/libc/hash/hashhl.c:42,
                  from /fsimages/usr/src/lib/libc/hash/md2/md2hl.c:17:
/usr/include/machine/_types.h:57: error: syntax error before "__int_least8_t"
In file included from /fsimages/usr/src/tools/compat/compat_defs.h:32,
                  from nbtool_config.h:526,
                  from /fsimages/usr/src/tools/compat/namespace.h:9,
                  from /fsimages/usr/src/lib/libc/hash/hashhl.c:42,
                  from /fsimages/usr/src/lib/libc/hash/md2/md2hl.c:17:
/usr/include/sys/types.h:72: error: syntax error before "int8_t"
In file included from /usr/include/inttypes.h:22,
                  from /fsimages/usr/src/tools/compat/compat_defs.h:59,
                  from nbtool_config.h:526,
                  from /fsimages/usr/src/tools/compat/namespace.h:9,
                  from /fsimages/usr/src/lib/libc/hash/hashhl.c:42,
                  from /fsimages/usr/src/lib/libc/hash/md2/md2hl.c:17:
/usr/include/sys/stdint.h:71: error: syntax error before "int_least8_t"

*** Failed target:  md2hl.lo
*** Failed command: cc -O -I. -I./include -I/fsimages/usr/src/tools/compat 
-DHAVE_NBTOOL_CONFIG_                H=1 -D_FILE_OFFSET_BITS=64 
-D__DBINTERFACE_PRIVATE -c -o md2hl.lo.o /fsimages/usr/src/tools/comp 
at/../../lib/libc/hash/md2/md2hl.c
*** Error code 1

~BAS