1. Code uses PPC_FEATURE_HAS_VSX, but it's not checked similarly to
PPC_FEATURE2_ARCH_3_00 and PPC_FEATURE2_ARCH_3_00 for availability. FreeBSD has
those macros in machine/cpu.h, but I went with the way chosen for
PPC_FEATURE2_ARCH_3_00 and PPC_FEATURE2_ARCH_3_00. Other than that, FreeBSD also
has sys/auxv.h and that's where elf_aux_info() is defined.
2. getauxval() is actually Linux-only, but code checked for __unix__. It won't
work on all UNIX, so change it back to __linux__. Add another code variant
strictly for FreeBSD.
3. Update comment. This commit adds code for FreeBSD, but recently there
appeared support for powerpc64 in OpenBSD.

* fix: correctly check neon flags for QNX platform

* refactor: change __QNXNTO__ to __QNX__

* backport elementwise_layers refactor

* keep NULL

Some older compilers do not allow to pass a `const int` as an immediate. Use an unnamed enum instead.

Error was "Input parameters must be a matrices!", but "matrices" is plural and doesn't allow the unspecific article "a".

* Add SymmColumnVec_32f8u

* Fix double to float warnings

* Fix gst error handling

* Use the return value instead of the error, which gives no guarantee of being NULL in case of error
* Test err pointer before accessing it
* Remove unreachable code

* videoio(gstreamer): restore check in writer code
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

- prevent running code over unsupported/non-tested configurations
- prevent integer div by zero

Fix ORB integer overflow

* set size_t step to fix integer overflow in ptr0 offset

* added issue_537 test

* minor fix tags, points

* added size_t_step and offset to remove mixed unsigned and signed operations

* features2d: update ORB checks
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

* dnn: fix unaligned memory access crash on armv7

The getTensorContent function would return a Mat pointing to some
member of a Protobuf-encoded message. Protobuf does not make any
alignment guarantees, which results in a crash on armv7 when loading
models while bit 2 is set in /proc/cpu/alignment (or the relevant
kernel feature for alignment compatibility is disabled). Any read
attempt from the previously unaligned data member would send SIGBUS.

As workaround, this commit makes an aligned copy via existing clone
functionality in getTensorContent. The unsafe copy=false option is
removed. Unfortunately, a rather crude hack in PReLUSubgraph in fact
writes(!) to the Protobuf message. We limit ourselves to fixing the
alignment issues in this commit, and add getTensorContentRefUnaligned
to cover the write case with a safe memcpy. A FIXME marks the issue.

* dnn: reduce amount of .clone() calls

* dnn: update FIXME comment
Co-authored-by: NAlexander Alekhin <alexander.a.alekhin@gmail.com>

features2d: repair SimpleBlobDetector

* features2d: revert code change by PR #19859

Reverted commit 76860933

* features2d: check SimpleBlobDetector parameters consistency