gdcm FTBFS with vtk 9.6 (in experimental) and gcc 15.3.0

FAILED: [code=1] Utilities/VTK/Applications/CMakeFiles/gdcm2pnm.dir/gdcm2pnm.cxx.o
/usr/bin/x86_64-linux-gnu-g++ -DFMT_SHARED -DGLAD_API_CALL_EXPORT -DSCN_DISABLE_FAST_FLOAT=0 -DSCN_DISABLE_REGEX=0 -DSCN_REGEX_BACKEND=0 -Dkiss_fft_scalar=double -DvtkRenderingCore_AUTOINIT_INCLUDE=\"/home/drew/projects/misc/build/vtk-dep/gdcm-3.0.24/obj-x86_64-linux-gnu/CMakeFiles/vtkModuleAutoInit_ef581ebbf3812c41155eb6cbf7fd17d1.h\" -I/build/vtk-dep/gdcm-3.0.24/obj-x86_64-linux-gnu/Source/Commo
n -I/build/vtk-dep/gdcm-3.0.24/Source/Common -I/build/vtk-dep/gdcm-3.0.24/Source/DataStructureAndEncodingDefinition -I/build/vtk-dep/gdcm-3.0.24/Source/MediaStorageAndFileFormat -I/build/vtk-dep/gdcm-3.0.24/Source/DataDictionary -I/build/vtk-dep/gdcm-3.0.24/obj-x86_64-linux-gnu/Utilities/VTK -I/build/vtk-dep/gdcm-3.0.24/Utilities/VTK -isystem /usr/include/vtk-9.6 -isystem /usr/include/vtk-9.6/vtkfmt -isystem /usr/include/vtk-9.6/vtkscn/include -isystem /usr/include/vtk-9.6/vtkscn -isyste
m /usr/include/vtk-9.6/token -isystem /usr/include/vtk-9.6/vtkkissfft -isystem /usr/include/freetype2 -isystem /usr/include/vtk-9.6/vtkglad -g -O2 -ffile-prefix-map=/build/vtk-dep/gdcm-3.0.24=. -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -Wdate-time -D_FORTIFY_SOURCE=2 -std=gnu++20 -MD -MT Utilities/VTK/Applications/CMakeFiles/gdcm2pnm.dir/gdc
m2pnm.cxx.o -MF Utilities/VTK/Applications/CMakeFiles/gdcm2pnm.dir/gdcm2pnm.cxx.o.d -o Utilities/VTK/Applications/CMakeFiles/gdcm2pnm.dir/gdcm2pnm.cxx.o -c /build/vtk-dep/gdcm-3.0.24/Utilities/VTK/Applications/gdcm2pnm.cxx
/build/vtk-dep/gdcm-3.0.24/Utilities/VTK/Applications/gdcm2pnm.cxx: In function ‘int main(int, char**)’:
/build/vtk-dep/gdcm-3.0.24/Utilities/VTK/Applications/gdcm2pnm.cxx:33:10: error: ‘cerr’ is not a member of ‘std’
   33 |     std::cerr << argv[0] << " input.dcm output.pnm" << std::endl;
      |          ^~~~
/build/vtk-dep/gdcm-3.0.24/Utilities/VTK/Applications/gdcm2pnm.cxx:22:1: note: ‘std::cerr’ is defined in header ‘<iostream>’; this is probably fixable by adding ‘#include <iostream>’
   21 | #include "vtkMedicalImageProperties.h"
  +++ |+#include <iostream>
   22 |


Not sure why there's a change in behaviour. It had already been
building with -std=gnu++20.


Just needs #include <iostream> added.