Convert several preformatted code block literals that enumerate lists of
options or variables to use reST definition lists instead.  Manually
wrap other long lines in code blocks.

Make sure these modules also include exactly the version shipped with CMake.

Fixes issues #14812 and #14813 where find_package(OpenMP QUIET) and
find_package(Qt4 QUIET) would still print out messages when calling
check*() functions.

Also a partial fix for  #14445 where building CMake
(without cmake-gui) when Qt5 is installed and Qt4 is not installed
and warnings come out of FindQt4.cmake.

Avoid saying "... detected in default set..." each time CMake is run.

Prompted by Rolf Eike Beer on cmake-developers@.

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@.