Output parsers: Replace the chaining approach

Use "flat" aggregation instead.
This is another step towards the formatter/parser merger.
Along the way, also fix some some subclasses (mostly in BareMetal) that
erroneously forwarded handled output to other parsers.

Task-number: QTCREATORBUG-22665
Change-Id: I12947349ca663d2e6bbfc99efd069d69e2b54969
Reviewed-by: hjk <hjk@qt.io>

src/plugins/ios/iosbuildstep.cpp

@@ -223,9 +223,7 @@ bool IosBuildStep::init()
     setIgnoreReturnValue(m_clean);
 
     setOutputParser(new GnuMakeParser());
-    IOutputParser *parser = target()->kit()->createOutputParser();
-    if (parser)
-        appendOutputParser(parser);
+    appendOutputParsers(target()->kit()->createOutputParsers());
     outputParser()->addSearchDir(pp->effectiveWorkingDirectory());
 
     return AbstractProcessStep::init();