Pretty-printers: Quickfix for QMap from Qt5

Unfortunately if one of the printers for a member fails, the complete
class cannot be displayed in the debugger. So let's just fall back to
the default printer in case we do not support the type (here: QMap from
Qt5)

CCBUG: 331044
Pretty-printers: Simplify printer for QString
Force debugging-mode compile flags for debuggees

"set(CMAKE_BUILD_TYPE Foo)" in some subdirectory is known to
cause troubles -- and it does so on the frameworks branch. Debuggees are
not compiled in debug mode there.

Fix it by explicitly overwriting compile flags for debuggee targets.

See: http://public.kitware.com/Bug/view.php?id=14634
Show "catch throw" for exceptions with missing 'original-location'
field.

This could happen with gdb 7.7.
Note that if there be more cases with missing 'original-location'
field, we should show the breakpoint's address then (even though
it's not so useful, but it's better then showing nothing at all...)
Use the same FindQJson.cmake like in kdevplatform

Let's see if this fixes build on CI.