- 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

Write defines into a disk file instead of passing 100s of them on the command line directly. Fixes some issues with build commands on my machine, and makes it a lot easier to view the make VERBOSE=1 output.

Add mbed-create-distro

CMake: Enable improved armclang support in CMake 3.21 ...

CMake versions 3.20 and below always add compiler and linker flags
based on `CMAKE_SYSTEM_PROCESSOR`, for example `--cpu=Cortex-M33`.
This sometimes overrides flags we set in tools/cmake/cores/*.cmake
and results in link failure or unbootable binaries. To workaround
this, we added more linker flags to "counter" what CMake automatically
adds.

From CMake 3.21 onwards, CMake by default does not add flags to
armclang anymore, and it fully relies on projects to set all flags.
In this case we do not need to set `CMAKE_SYSTEM_PROCESSOR` or use
workarounds anymore. We still turn on workarounds when an older
version of CMake (3.19 and 3.20) is used, but in the future we might
require users to have at least CMake 3.21.

CMake: Move post build functions out of root CMakeLists.txt ...

The 'post build' functions are made visible by adding the mbed-os
subdirectory. This is not ideal as any components in mbed-os wishing to
call the functions must be added after the functions are defined. To
improve modularity move these functions to a separate CMake script.

We include the post build CMake script in app.cmake for now so we don't
break user's projects.

app.cmake: Replace tabs with spaces ...

The coding standards of Mbed OS require indentation of four spaces.

CMake: set CMAKE_MODULE_PATH in the Mbed OS CMakelists.txt ...

Update CMAKE_MODULE_PATH at once place.

Note, we update also CMAKE_MODULE_PATH in app.cmake. This is temporary until we get a proper way to include
Mbed Os (removing app.cmake need to be included by an application).

CMake: add mbed_ prefix to our CMake files ...

To avoid conflicts as we expose our CMake list files via CMAKE_MODULE_PATH. Some files already include it, this
aligns the rest of files.

I leave app.cmake as it is - it's user facing and it would be breaking change. We can clean this one for the next major version.

CMake app: add our cmake folder to CMAKE_MODULE_PATH ...

All files within tools/cmake can now include within tools/cmake. We do not expose
internal folders like core/profiles/toolchains.
They should be included via toolchain file (mbed_toolchain in our case).

CMake tools: use CMAKE_CURRENT_LIST_DIR instead of MBED_PATH ...

Excluding greentea tests, they will be fixed separately (more work needed).

Rebase against master

Whitespace formatting changes.

Add extra lines as requested

Parse requirements.txt in CMake

Add FindPythonPackage and use it to detect memap dependencies

Add newline

Set executable suffix in CMake

Rebase linker script change properly, re-add external toolchain file support

Change toolchain file to load core and toolchain options *before* compilers are loaded.

CMake: Fix error that prevented re-build ...

Promote MBED_TOOLCHAIN_FILE_USED to cache variable so
its previous state can be recalled when re-building. This
is because CMAKE_TOOLCHAIN_FILE is also a cache variable and its
value is set on first run when it has not been set.

CMake: Fix third party toolchain file suppport ...

Compile defintions are always included. However, functions that set compile options
are only called if a third party toolchain file is not used

CMake: Rename Mbed OS path variable for consistency ...

Rename the CMake variable expected from applications from MBED_ROOT to
MBED_PATH to be consistent with the naming used for the configuration file
(MBED_CONFIG_PATH) also expected from applications.

Activate ccache for CMake

CMake: fix application config ...

These settings like enable_language should be done in the application and just once.
We hit the issue when you expose sources to an app (interface or public), CMake errors as some of the internal settings have not been configured.