Libidn2 2.34 MinGW build failure

Building the MinGW CI docker image fails with libidn2 2.34 (2.33 worked fine).

Looking into the reveals a chain of two issues.

The first issue is that unistring/ is built though libunistring is installed. The configure script even finds and reports it with

Libunistring:      yes 1.0.0 -L/usr/local/x86_64-w64-mingw32/lib -lunistring -L/usr/local/x86_64-w64-mingw32/lib -liconv -R/usr/local/x86_64-w64-mingw32/lib

I would expect that libunistring is linked in and thus unistring/ doesn't need to be built. I just might not be able to remeber the reason for this right now.

The second issue is that building `unistring/' fails with

uninorm/nfc.c:25:41: warning: 'uninorm_nfc' redeclared without dllimport attribute: previous dllimport ignored [-Wattributes]
   25 | const struct unicode_normalization_form uninorm_nfc =
      |                                         ^~~~~~~~~~~
uninorm/nfc.c:30:5: error: initializer element is not constant
   30 |     &uninorm_nfd
      |     ^
uninorm/nfc.c:30:5: note: (near initialization for 'uninorm_nfc.decomposing_variant')
make[3]: *** [Makefile:2232: uninorm/libunistring_la-nfc.lo] Error 1

The dockerfile is https://gitlab.com/gnuwget/build-images/-/blob/master/docker-debian-mingw/Dockerfile
(Using docker build -f <Dockerfile> . reproduces the error.)

The build output is output.txt