Mark qt_assert and qFatal as non-returning functions (excpt. MSVC)

Mark qt_assert and qFatal as non-returning functions (excpt. MSVC)

This allows the compiler to optimise the code a bit better: since they
don't return, it can assume in the code after the Q_ASSERT that the
condition was true.

MSVC is the exception: with MSVC, we have the CrtDbgReport dialog,
which allows the developer to continue execution, inside the
debugger. Therefore, we can't mark any of those functions as
non-returning because they can, after all, return.

Unfortunately, the Q_ASSERT usually expands to no code in release
mode, so the improvement in code generation happens in debug mode
only...

Change-Id: I4d542d6853cd51c71ffab1d563ed64ef7c419115
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>