WIP: `Array_slices` check for valid result, and more flexible Makefile

[TApplencourt]

Hi,

First Thanks a lot for this repo! I work at ALCF, and I plan to use this repo to strengthen our IFX (the new Intel Fortran compiler) story.

To do so, I did a few modifications to the codebase. Right now it's only in the array_slices folder. I make this PR to see if you are interested to collaborate to merge it.

2 "big" change:

• Update Makefile to pickup FC / FCFLAGS (so people can show with a compiler to use). I also change the makefile to be ~incomprehensible~ more general and those it also runs the job (so make will compile and run; make exe will just create the executible), but this can be reverted back.
• Add some checks to verify the results is correct.

I'm open to make any change to this PR to make live easier for you, Thanks a lot for writing those tests,

Regards, Thomas

[aaroncblack]

Thanks @TApplencourt! I apparently do not have my GitHub notifications enabled, took me quite a while to check this repo and see your PR.

[TApplencourt]

No problem at all.
Sorry for the messy PR! I did remove some code that wasn't necessary for our compiler (some ISO c binding, and some Cuda code), I'm not sure if you want to keep those changes.

I understand if you don't want to merge this PR and that maybe you don't want to have the BW to support this repo anymore. But if you are interested I can try to cherry-pick some changes, and to make more smaller individual PR. Or maybe the best course of action is to try to merge your nice tests into https://github.com/SOLLVE/sollve_vv.