• removed the old branch with non-standard rounding completely
• enable the use of GCC/clang __builtin_*() functions more broadly; now it's not limited to x86, x64, arm and PPC64 archs. Actually, before this patch some of __builtin_*() have been used only inside PPC64 branch. Now they are used everywhere. We assume that GCC/clang provide the necessary intrinsics on all target platforms.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

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