build error: namespace "std" has no member "is_same_v"

Hello.
Just pulled ngsolve and trying to build, first using gcc and then icpc
both compilers give the same error below.
I tried -std=c++11 and -std=c++17 . any ideas?
Thanks
Peter

Netgen 6.2-20203: Automatic configuration OK.

Build type: Release
Flags: -O3 -DNDEBUG -std=c++17

Enabled functionality:

OCC: ............... OFF
JPEGlib: ........... OFF
FFMPEG: ............ OFF
GUI: ............... ON
MPI: ............... OFF
PYTHON: ............ ON


make
[ 3%] Performing build step for 'netgen_project'
[ 10%] Performing check_submodules1 step for 'netgen'
[ 20%] Performing build step for 'netgen'
[ 1%] Building CXX object libsrc/core/CMakeFiles/ngcore.dir/archive.cpp.o
In file included from /home/peter/software/ngsolve-src/external_dependencies/netgen/libsrc/core/archive.hpp(20),
from /home/peter/software/ngsolve-src/external_dependencies/netgen/libsrc/core/archive.cpp(2):
/home/peter/software/ngsolve-src/external_dependencies/netgen/libsrc/core/type_traits.hpp(42): error: namespace "std" has no member "is_same_v"

Hi,
which version of gcc do you use, or of the std library?
A cpp17 compatible version should provide std::is_same_v, I guess you have a version that does not fully support cpp17.
en.cppreference.com/w/cpp/types/is_same
Best
Christopher