[exim] compile problems: exim + spf (libspf2)

hi folks,

I tried to compile exim 4.71 (also tried 4.69) with different versions of
libspf2 (1.2.{9,8,7,6}) (compiled versions + 1.2.9 as a package from OpenBSD).
Platform is OpenBSD 4.5 (amd64).

This is the problem:
BEGIN TERMINAL OUTPUT:
# make
`Makefile' is up to date.

gcc exim_dbmbuild.c
In file included from /usr/local/include/spf2/spf_dns.h:113,
                from /usr/local/include/spf2/spf_server.h:22,
                from /usr/local/include/spf2/spf.h:27,
                from spf.h:17,
                from exim.h:449,
                from exim_dbmbuild.c:33:
/usr/local/include/spf2/spf_dns_rr.h:56: error: syntax error before "ns_type"
/usr/local/include/spf2/spf_dns_rr.h:77: error: syntax error before "ns_type"
In file included from /usr/local/include/spf2/spf_server.h:22,
                from /usr/local/include/spf2/spf.h:27,
                from spf.h:17,
                from exim.h:449,
                from exim_dbmbuild.c:33:
/usr/local/include/spf2/spf_dns.h:123: error: syntax error before "ns_type"
/usr/local/include/spf2/spf_dns.h:160: error: syntax error before "ns_type"
/usr/local/include/spf2/spf_dns.h:163: error: syntax error before "ns_type"
/usr/local/include/spf2/spf_dns.h:166: error: syntax error before "ns_type"
In file included from spf.h:17,
                from exim.h:449,
                from exim_dbmbuild.c:33:
/usr/local/include/spf2/spf.h:81: error: syntax error before "rr_type"
*** Error code 1

Stop in /home/software/exim-4.71/build-OpenBSD-amd64 (line 603 of Makefile).
*** Error code 1

Stop in /home/software/exim-4.71 (line 31 of Makefile).
END TERMINAL OUTPUT

The Makefile contains:
EXPERIMENTAL_SPF=yes
CFLAGS += -I/usr/local/include
LDFLAGS += -L/usr/local/lib -lspf2

I tried to fix the problem, but did not succeed. Without SPF it works fine.

Thank you for any help.

Merry Christmas!

Cheers,
Vincent