Test: fixing itoa implementation and clean-up of tests and test Makefile (#8531)

* Test: fixing itoa implementation, clean-up of tests and test runner

Update itoa to be the same as newlib, fixing edgecase of abs(INT_MIN)
Update WString.cpp:toString() integer conversions to use noniso funcs
Remove legacy gcc versions from Makefile and allow overrides
Don't fallback to c11 and c++11, source cannot support that

* CXX and CC are make predefined values, assuming ?= does not work (?)

tests/host/common/ArduinoCatch.hpp

@@ -0,0 +1,36 @@
+/*
+ Arduino.cpp - Mocks for common Arduino APIs
+ Copyright © 2016 Ivan Grokhotkov
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy
+ of this software and associated documentation files (the "Software"), to deal
+ in the Software without restriction, including without limitation the rights
+ to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ copies of the Software, and to permit persons to whom the Software is
+ furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in
+ all copies or substantial portions of the Software.
+*/
+
+#include <Arduino.h>
+#include <sys/time.h>
+
+#include <ostream>
+
+#include "catch.hpp"
+
+// Since Catch does not know about Arduino types, help it out so we could have these displayed in the tests output
+
+std::ostream& operator<<(std::ostream&, const String&);
+
+namespace Catch {
+
+std::string toString(const String&);
+
+template<>
+struct StringMaker<String> {
+    static std::string convert(const String&);
+};
+
+} // namespace Catch