Update the helper files so that the library can be compiled with newer compilers

[shibatch]

Checklist

• I have read the contributing guidelines.
• I have considered portability of my change across platforms and architectures.
• I have self-reviewed my code.
• I have commented my code where necessary.
• I have updated the documentation accordingly.
• I have added tests that prove my fix is effective or that my feature works.

What is the purpose of this pull request?

• This update is required to build the library with newer compilers, especially MSVC.

What changes did you make?

• Notation like ((vdouble) { +0.0, -0.0, +0.0, -0.0 }) is not compliant to the standards, and had to be replaced with vector-set intrinsics.
• Added explicit typecasting so that the code can be compiled with C++ which has strict type checking.

Does this PR relate to any existing issue?

This is part of the patches that implements #574.

[blapie]

Sorry, I was just testing the new compatibility checks, if you rebase your change these 2 checks should pass now.