Add FindBacktrace.cmake module.

It designed to search for implementation of backtrace(3) routine.
Currently it is used in OpenBSD Ports for building Clementine
music player.

A lot of input from brad.king@ and neundorf@.
Credit Kitware and csimsoft for their maintenance roles

Add maintenance credit to command-line "--version" output and the
cmake-gui "About" dialog.
FindwxWidgets: Add support for wxWidgets 3.0.0 (#14587)

Add the "wxWidgets-3.0.0" path suffix and the "30" library names.
While at it, add the "wxWidgets-2.9.5" suffix too.
Add policy CMP0040 to disallow custom commands on missing targets
Merge topic 'find_backtrace'

c6f339c Add FindBacktrace.cmake module.
Merge topic 'FindwxWidgets-3.0.0'

2cd5597 FindwxWidgets: Add support for wxWidgets 3.0.0 (#14587)
Merge topic 'cmake-credits'

6fc4ab9 Credit Kitware and csimsoft for their maintenance roles
Merge topic 'missing-target-error'

a02f3d2 Add policy CMP0040 to disallow custom commands on missing targets