ISA 2.07 (aka POWER8) effectively extended the expanding multiply
operation to word types. The altivec intrinsics prior to gcc 8 did
not get the update.

Workaround this deficiency similar to other fixes.

This was exposed by commit 33fb253a
which leverages the int -> dword expanding multiply.

This fixes Issue #15506

ffmpeg: 4.1.3 -> 4.2.1
libvpx: 1.8.0 -> 1.8.1

  - add comments on signature of custom parallel_for
  - use cv::parallel_for_ by default

* Added mechanism to set/toggle NORMAL window to TOPMOST window.

* highgui: remove unnecessary/legacy code

* Adding all possible data type interactions to the perf tests since some
use SIMD acceleration and others do not.

* Disabling full tests by default.

* Giving proper names, removing magic numbers and sanity checks of new
performance tests for the integral function.

* Giving proper names, making array static.

* fix 'chmod' is not recognized as an internal or external command in Windows

https://github.com/opencv/opencv/issues/14939

* cmake: update PCH command handling

* Wrap unsupported by IE layers as custom layers

* Replace pointers to layers blobs to their shapes

* Enable Faster R-CNN with IE backend on CPU

- error: variables in the local address space can only be declared in the outermost scope of a kernel function