This patch updates helpers for ppc64el, s390x and purec_scalar.

[shibatch]

It adds explicit typecasting so that C++ compilers can compile the inline headers generated from these helpers.

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 patch addresses the problem where the inline headers for ppc64el, s390x and purec_scalar cannot be compiled with C++ compilers.

What changes did you make?

This patch updates helpers for ppc64el, s390x and purec_scalar.
It adds explicit typecasting so that C++ compilers can compile the inline headers generated from these helpers.

Does this PR relate to any existing issue?

This is part of the patches that implements #574.

[blapie]

Hello! Aren't there intrinsics for power and s390x that could handle these operations in a vector fashion directly?

[shibatch]

They were not available when I wrote those helpers.
They may be there now though.
I tried everything I could at the time.
Unlike Intel and ARM, reference manuals were not well maintained at that time, so I remember having a lot of trouble.

[blapie]

Hm, ok. That's what I thought. It would be good to find someone that can look into these in the future.

Feel free to merge, so at least we can use inline headers in C++.