dev build problem

The current dev 9e35973fb6c0 would not build on Fedora:

make V=1:

ibtool: compile:  g++ -DHAVE_CONFIG_H -I. -I.. -DOCTINTERP_DLL -Iliboctave
-I../liboctave -I../liboctave/array -Iliboctave/numeric
-I../liboctave/numeric -Iliboctave/operators -I../liboctave/operators
-I../liboctave/system -I../liboctave/util -I../libinterp/octave-value
-Ilibinterp -I../libinterp -I../libinterp/operators -Ilibinterp/parse-tree
-I../libinterp/parse-tree -Ilibinterp/corefcn -I../libinterp/corefcn
-I../liboctave/wrappers -I/usr/include/GraphicsMagick -fPIC -pthread
-fopenmp -Wall -W -Wshadow -Woverloaded-virtual -Wold-style-cast -Wformat
-Wpointer-arith -Wwrite-strings -Wcast-align -Wcast-qual
-fvisibility=hidden -O2 -march=native -mavx -mavx2 -MT
libinterp/dldfcn/audiodevinfo_la-audiodevinfo.lo -MD -MP -MF
libinterp/dldfcn/.deps/audiodevinfo_la-audiodevinfo.Tpo -c
../libinterp/dldfcn/audiodevinfo.cc  -fPIC -DPIC -o
libinterp/dldfcn/.libs/audiodevinfo_la-audiodevinfo.o
In file included from ./config.h:3181,
                 from ../libinterp/dldfcn/audiodevinfo.cc:27:
./oct-conf-post.h:27:32: error: expected declaration before ‘}’ token
   27 | #  define OCTAVE_NAMESPACE_END }
      |                                ^
../libinterp/dldfcn/audiodevinfo.cc:2849:1: note: in expansion of macro
‘OCTAVE_NAMESPACE_END’
 2849 | OCTAVE_NAMESPACE_END
      | ^~~~~~~~~~~~~~~~~~~~
make[2]: *** [Makefile:20152:
libinterp/dldfcn/audiodevinfo_la-audiodevinfo.lo] Error 1

this is with gcc version 11.2.1 20210728 (Red Hat 11.2.1-1) (GCC).
A similar problem with clang 12.0.1.
See also buildbot logs.

Dmitri.
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