* 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 (?)
