Changes time-integration scheme parameters from variable to constexpr in timestepper library

[uumesh]

Parameters such as Nrk and Nstages are declared as variables in the timestepper library with values assigned in the member functions. And these variables are used to define array sizes at runtime which gives compilation errors while building with Intel compilers.

To resolve the issue, these parameters are modified and defined as static constexpr with fixed values in the timeStepper.hpp header file.

[noelchalmers]

Not sure why the CI didnt trigger on this. Anyone know how to trigger it?

[nnnunnn]

Does the Intel compiler-in-question not implement C99 variable length arrays? (Visual C++ 2019 does not.)

[uumesh]

I was trying to build and test with the icpx compiler that comes with the latest Intel oneAPI toolkit. Although, it does support the C99 VLA feature, it does not allow me to compile with this option.

For example, trying a test code, I get the following error

icpx --std=c99 test.cpp 
warning: invalid argument '--std=c99' not allowed with 'C++/ObjC++'
test.cpp:6:9: error: variable-sized object may not be initialized
  int a[N] = {1,2,3,4,5};
        ^

[nnnunnn]

I get the same with Visual C++. Its C compiler compiles C99 VLA's, but these are rejected by the C++ compiler. Sounds like Intel has taken the same approach?