Build system fixes on linux

[reos-rcrozier]

Feature or improvement description Fixes issues with installing and building on Linux, especially simulink interface

Impacted areas of the software Build system

Additional supporting information Installing the C++ interface failed on linux due to a typo in the file named SC.h in CMakeLists.txt I have changed it from SC.H -> SC.h This problem probably doesn't show up on windows as it's file system is case insensitive

I also fixed an issued with building the simulink S-Function on linux. mex on linux does not use COMPFLAGS, you must use CFLAGS or CXXFLAGS, also the -MT option does something very different in gcc than visual studio C++

[rafmudaf]

@bjonkman could you review these changes to the Simulink API build system?

[reos-rcrozier]

@rafmudaf all tests passing on this branch for me see results here

Can we consider merging please?

[andrew-platt]

@reos-rcrozier, I'll merge this as soon as GH actions completes. These changes should make no difference to GH since it is just in the create_sfunc.m that isn't run in testing.

I'm letting the tests run mostly to see if I can learn anything about why GH actions is failing for us.

[reos-rcrozier]

OK, thanks!

[andrew-platt]

I rebased this PR and merged. Thanks for contributing, and thank you for your patience.