ddd @3.3.12_3 build: LabelH.C error: unknown type name 'a_class'; did you mean 'class'?

[p-bro]

ddd fails to build on High Sierra (10.13.1) after a migration upgrade from El Capitan. The first error appears in the build process, when compiling LabelH.C, while including an Xcode file:

/usr/bin/clang++ -DHAVE_CONFIG_H -I.  -I./..  -I/opt/local/include  -Os  -Wall -W -Wwrite-strings -pipe -stdlib=libc++ -arch x86_64 -trigraphs  -MT LabelH.o -MD -MP -MF .deps/LabelH.Tpo -c -o LabelH.o LabelH.C
In file included from LabelH.C:36:
In file included from /opt/local/include/Xm/XmP.h:45:
In file included from /opt/local/include/Xm/Xm.h:59:
In file included from /opt/local/include/X11/Intrinsic.h:53:
In file included from /opt/local/include/X11/Xlib.h:51:
In file included from /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/stddef.h:51:
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include/c++/v1/__nullptr:35:15: error: unknown type name 'a_class'; did you mean 'class'?
    template <class _Tp>
              ^
LabelH.C:34:15: note: expanded from macro 'class'
#define class a_class
              ^

The full log from port -d install is attached. Xcode is at 9.1 (9B55).

[p-bro]

Output from port -d install ddd

[ryandesign (Ryan Carsten Schmidt)]

The error was already reported to the developers:

​https://savannah.gnu.org/bugs/?52175

So far, they have not responded.

[ryandesign (Ryan Carsten Schmidt)]

In a71fa9f497ef9e7b18dbfa163952d4d5e6123600/macports-ports:

ddd: Fix build with Xcode 9

Include stddef.h early, before it is included as a side-effect of
including the Motif headers, while class has been redefined as
a_class, with which the system headers are no longer ok.

Closes: #55342