C++: Use soft asserts in CppRewriter

While a "real" C++ type rarely contains parantheses or other
characters that are "special" for a regexp, gdb happily
sprinkles in things like "(anonymous namespace)::".

Killing Creator while trying to beautify such a name
is inaccpetable.

This should be followed up by patches handling the known
problematic cases properly.

Change-Id: I8cc8509f1d7df0a8780876cdba556e1cf7ec4a95
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@nokia.com>