- Split mbed-core and mbed-rtos into -sources and -flags targets ...

- Fix some logic errors in top level cmakelists related to building greentea tests
- Fix mbed_create_distro() for OBJECT libraries

CMake: Update mbed os, unittest CMake and add CMAKE_CROSSCOMPILING guard ...

- Add a new MbedOS project in mbed os root CMake which can be used along with
  BUILD_TESTING conditional check for enabling the unittest build
- Update UNITTEST CMake for setting the CMake configuration like c, cxx flags etc.,
- Add if CMAKE_CROSSCOMPILING conditional check wherever target configuration check
  and toolchain configuration to avoid such configuration gets included for unittest build.

CMake: remove IAR references as they are not supported

CMake: add mbed-os and mbed-baremetal targets ...

mbed-os consists of mbed-core and mbed-rtos
mbed-baremetal consists of mbed-core

The main change is for mbed-core. Changing from object library to be interface. This way it allows us to do the above to have 2 main targets for users to use.

This should be backward compatible change as mbed-os target we used contains the same files/options as previously set.

CMake: split rtos from core target ...

Add or remove and directories containing source files, header files, and macro definitions that implement RTOS support.
This includes:
- cmsis/CMSIS_5/CMSIS/RTOS2/
- cmsis/device/rtos/
- rtos/source/ConditionVariable.cpp
- rtos/source/Thread.cpp

CMake: Rename CMake targets ...

* mbed-os renamed mbed-core
* mbed-os-<COMPONENT> renamed mbed-<COMPONENT>

CMake: Restore rtos api and netsocket presence macro names ...

The old tools rely on the old names to build

CMake: Fix build failure due to CMSIS restructure