Compile error on `x11/cde` on OpenBSD 7.6 and up

[ekollof]

x11/cde no longer builds on OpenBSD 7.6 and up.

/usr/local/bin/libtool  --tag=CXX   --mode=compile c++ -DHAVE_CONFIG_H -I. -I../../../include   -I/usr/local/include -DANSICPP -DMULTIBYTE -DNLS16 -DCSRG_BASED -DUSE_XINERAMA -DUSE_XRENDER  -DEXPAND_TEMPLATES -DCDE_NEXT -I.. -O2 -pipe -Wno-unused-result -Wno-write-strings -fno-strict-aliasing      -I/usr/X11R6/include  -pthread -MT libStyleSheet_la-SSPath.lo -MD -MP -MF .deps/libStyleSheet_la-SSPath.Tpo -c -o libStyleSheet_la-SSPath.lo `test -f 'SSPath.C' || echo './'`SSPath.C
libtool: compile:  c++ -DHAVE_CONFIG_H -I. -I../../../include -I/usr/local/include -DANSICPP -DMULTIBYTE -DNLS16 -DCSRG_BASED -DUSE_XINERAMA -DUSE_XRENDER -DEXPAND_TEMPLATES -DCDE_NEXT -I.. -O2 -pipe -Wno-unused-result -Wno-write-strings -fno-strict-aliasing -I/usr/X11R6/include -pthread -MT libStyleSheet_la-SSPath.lo -MD -MP -MF .deps/libStyleSheet_la-SSPath.Tpo -c SSPath.C  -fPIC -DPIC -o .libs/libStyleSheet_la-SSPath.o
In file included from SSPath.C:31:
In file included from ./SSPath.h:27:
In file included from ./SymTab.h:32:
In file included from ../dti_cc/cc_hdict.h:29:
In file included from ../dti_cc/cc_pvect.h:57:
In file included from ../dti_cc/cc_pvect.C:25:
In file included from ../dti_cc/cc_exceptions.h:28:
In file included from /usr/include/c++/v1/fstream:186:
In file included from /usr/include/c++/v1/__locale:18:
In file included from /usr/include/c++/v1/mutex:192:
In file included from /usr/include/c++/v1/__mutex_base:20:
In file included from /usr/include/c++/v1/system_error:154:
In file included from /usr/include/c++/v1/string:576:
In file included from /usr/include/c++/v1/string_view:1025:
In file included from /usr/include/c++/v1/algorithm:1920:
In file included from /usr/include/c++/v1/iterator:684:
In file included from /usr/include/c++/v1/__iterator/common_iterator.h:30:
/usr/include/c++/v1/variant:532:39: error: too few arguments provided to function-like macro invocation
    return __at(__fmatrix, __vs.index()...)(
                                      ^
/usr/X11R6/include/X11/Xos.h:67:12: note: macro 'index' defined here

Looks like something is clashing?