QNX Neutrino support

[SSE4]

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there is some existing demand for QNX Neutrino support: https://github.com/conan-community/community/issues/78 https://github.com/conan-io/conan/issues/2970

add an official support for QNX Neutrino operation system. it means, at least, the following:

• define new OS in settings.yml (name might be QNX or Neutrino)
• define OS versions, at least 6.5, 6.6, 7.0
• define new compiler - QCC, and its versions (4.2.2, 5.4.0)
• add standard libraries for QNX/QCC: gpp (GNU C++), cpp (Dinkum C+) and its variations (like Embedded Dinkum C++, Dinkum Abridged C++, etc)
• define GNU triplets for QNX cross-compiling (check config.guess)
• add required changes to the CMake helper (see https://cmake.org/cmake/help/v3.1/manual/cmake-toolchains.7.html#id9)

probably nice to have, but hard without access to the actual system - I doubt we will add it, as we mainly targeting cross-compiling from Windows/Linux/OSX to QNX, not running conan on QNX itself:

• add detection for QNX OS and compiler

/cc @jpovedano @Johnnyxy (as requestors)

[memsharded]

Merged, will be released in Conan 1.16