Remove independent doc listing for Qt4ConfigurationSettings, Qt4Macros
and UseQt4. These are implementation details.
Recommend the use of IMPORTED targets.
Remove references to the UseQt4 file, which is obsolete in light of
the IMPORTED targets.
Add documentation for automatic tool invocation and options.
Remove reference to variables which should not be needed in modern
implementations.
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@.