Clean up top-level build file and build options, fix build issues on MinGW

Update rtos CMake to include greentea test dir

CMake: Add option to enable greentea tests ...

Add an option to enable the greentea tests independently from the unit
tests.

We can't just use the typical BUILD_TESTING option to enable greentea
tests. BUILD_TESTING enables unit tests and fetches googletest, which
are compiled for the host. Greentea tests are cross compiled and require
a toolchain file. For this reason we add a new option just to enable
greentea tests, preventing build failures triggered by the unit tests
and googletest.

CMake: Move rtos stubs sources to the mbed-os/rtos directory ...

Move the rtos stub library into the rtos component directory.
so we can avoid duplicating the mbed-os source tree in a central
UNITTESTS folder.

CMake: Use relative paths to list source files and directories ...

The absolute path is still required for listing linker
files as they are referenced from a function in the top
level CMake input source file.

Update rtos/CMakeLists.txt ...

Co-authored-by: Hugues Kamba <41612201+hugueskamba@users.noreply.github.com>

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 present inclusion ...

We use only _PRESENT macros for components if they are enabled. Use the same in
the mbed.h file or anywhere else.

CMake: Componentize Mbed OS into multiple CMake targets (#13732) ...

Aside from the core mbed-os CMake target, a number of targets have been created so they can optionally be included by application executables that require them using `target_link_libraries()`.

Co-authored-by: Martin Kojtal <martin.kojtal@arm.com>
Co-authored-by: Rajkumar Kanagaraj <rajkumar.kanagaraj@arm.com>

CMake: Fix build failure due to CMSIS restructure

CMake: Fix CI error due to dir restruct of rtos and storage dirs

CMake: Fix failure due to restructure of rtos and ppp directories

CMake: Add support for rtos dir