NEC compiler warning in string_view

A user reported a compiler warning using NEC compilers

src/gromacs/modularsimulator/CMakeFiles/modularsimulator.dir/modularsimulator.cpp.o
"/gromacs-2020.1/src/gromacs/compat/string_view.h", line 894: error: incomplete type is not allowed
const basic_string_view v;

with the following settings

cmake ... -DCMAKE_C_COMPILER=mpincc -DCMAKE_CXX_COMPILER=mpinc++ -DCMAKE_C_FLAGS=" -report-all -fopenmp " -DCMAKE_CXX_FLAGS=" -report-all -fopenmp " -DGMX_MPI=ON -DCMAKE_PREFIX_PATH=/opt/nec/ve/nlc/2.0.0/ -DCMAKE_INSTALL_PREFIX=/S/home/nti/work/shubham/GROMACS_Intel/gromacs-2020.1/ -DGMX_DOUBLE=on -DFFTW_INCLUDE_DIR=/opt/nec/ve/nlc/2.0.0/include/ -DGMX_FFT_LIBRARY=fftw3 -DFFTW_LIBRARY=/opt/nec/ve/nlc/2.0.0/lib/

The associated user forum entry can be found here:

https://gromacs.bioexcel.eu/t/gromacs-installation-error/115