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

Fix missing GLOBAL_UP callback on successful connect ...

Fix an issue where CellularContext::do_connect_with_retry() does not call NSAPI_STATUS_GLOBAL_UP callback and validate_ip_address() on successful connect after failed try in blocking mode.

Fix missing GLOBAL_UP callback on successful connect ...

Fix an issue where CellularContext::do_connect_with_retry() does not call NSAPI_STATUS_GLOBAL_UP callback on successful connect after failed try in blocking mode.

modify method signatures to pass astyle tests

modify AT_CellularDevice_stub to pass test with the new feature

add the possibility to customize the delimiter of the ATHandler in ATCellularDevice class

NetworkStack: Remove stub implementations of socket_x_control ...

As a default implementation is already provided by
NetworkStack, stub implementations in the child classes
are not required. Furthermore, they return unsupported for
all cases instead of redirecting to the non-control API,
which is plainly wrong.

Code improvements for the unresolved comments ...

This patch contains improvements mentioned in the unresolved PR
comments:
- function names were changed from socket_sendmsg/socket_recvmsg to
  socket_sendto_control/socket_recvfrom_control.
- default implementation of this functions was provided in the
  NetworkStack class.
- MsgHeaderIterator accesses elements on the aligned addresses.

New feature: send/recv message implementation added to network stack

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.

Unit tests: Remove redundant CMake target mbed-headers-base ...

Individual libraries' `target_h` stub headers have now all been moved
from `mbed-headers-base` to `mbed-headers-<library>`.

Note: Even though headers previously in `target_h` are technically
stubs/fakes too, they are used by not only unit tests but also regular
libraries when compiled for unit tests, because no target-specific HAL
implementation exists in this case. In order for regular library
sources to pick up `target_h` headers, those headers must

* have the same names as regular headers
* appear first in include paths

This is why those headers are part of `mbed-headers-<library>` and not
`mbed-stubs-<library>`. Before this refactoring, `mbed-headers-base`
was the first in unit tests' include paths.

Unit tests: Fix style in cellular myCellularContext.h stub

Unit tests: Move cellular target_h stubs ...

We move test-specific files from the top-level UNITTESTS directory
into individual components' UNITTESTS/doubles subdirectories.

unittests: Remove ATHandler test interdependencies ...

Some tests in athandlertest.cpp relied on the state of stubs set in
previous tests. This caused test failures if the tests cases were ran in
isolation. Remove the interdependencies between tests by setting stub
values in the tests that rely on them.

CMake: unittests: Show all tests in CTest report ...

Previously a test executable was recognised as a single test by CTest.
However, test executables usually contain multiple test cases, the
results of the test cases should be individually reported. With our
previous setup we could miss test case failures that didn't cause the
executable to return an error code.

This commit uses gtest_discover_test to discover all test cases in a
test executable. This enables CTest to match test passes and failures
from the googletest binary output.

Remove mbed-headers-connectivity ...

Moved all the headers out of mbed-headers-connectivity, and these changes remove
that headers lib reference from lorawan and cellular unit tests

Merge pull request #14924 from ARMmbed/refactor_cellular_unittest ...

Refactor cellular unittest CMake

CMake: Limit cellular device cmake to use mocks/sources what it depends ...

Update cellular device unit tests CMake depends on a mock, which is
required for the test instead of depending on the group of mbed-stubs,
mbed-headers, mbed_stub_headers, libraries.
Limit the cellular context unit test CMake target_sources to keep only
required sources

CMake: Limit cellular common unit tests to use mocks what it depends ...

Update cellular common unit tests CMake depends on a mock, which is
required for the test instead of depending on the group of
mbed-headers libraries.

CMake: Limit at cellular unittest to use mock what it depends ...

Update AT cellular unit tests CMake depends on a mock, which is required
for the test instead of depending on the group of mbed-stubs,
mbed-headers, mbed_stub_headers, libraries.

AT command fix - hex string shouldn't be quoted on bc95

CMake: Add mbed-headers-nanostack-libservice library ...

Previously all nanostack libservice headers part of
mbed-headers-connectivity. This PR moves all the nanostack
libservice headers into newly added mbed-headers-nanostack-libraries.
This makes the nanostack libservice stubs more self-contained and
improves the composition of the library.

CMake: Remove mbed-stubs-rtos-headers library ...

- Previous changes moved all rtos stubs headers into mbed-stubs-rtos-headers
lib, but the decision to keep all stubs headers under the respective
component stubs library so moved all stubs rtos headers under
mbed-stubs-rtos and updated it depend component CMake
- Remove unnecessary add_definition call for UNITTEST as any of the stubs library
added from UNITTEST/CMakeLists.txt is not required this macro

Merge pull request #14873 from ARMmbed/move_connectivity_netsocket_stubs ...

Move connectivity netsocket stubs

Merge pull request #14773 from rwalton-arm/move_platform_stub ...

Move mbed-stubs-platform to the platform directory

Merge pull request #14884 from LDong-Arm/rm_UNITTEST_macro ...

Remove the `UNITTEST` macro from production code

Merge pull request #14835 from ARMmbed/move_stubs_cellular_headers ...

Move stubs cellular headers

CMake: Move netsocket stub headers to the netsocket doubles dir ...

Previously all the netsocket stubs headers under mbed-stubs-headers,
so this PR move all netsocket stubs headers under
netsocket/tests/UNITTESTS/double directory and update CMake to include
stubs headers into mbed-stubs-netsocket library to make netsocket stubs
to be self-contained.

CMake: Add mbed-headers-netsocket headers library ...

- Previously, all netsocket headers made as a part of the
mbed-headers-connectivity library. To make it easier to separate all
the netsocket headers into the separate mbed-headers-netsocket library
and keep them, as part of netsocket stubs CMake. This makes the
netsocket stubs more self-contained and improves the composition of the library.
- Update cellular, netsocket unit tests to link only with a mbed-headers-netsocket
library that it depends on instead of link with mbed-headers
which is a group of headers libraries.

CMake: Update netsocket, cellular unittest to use mbed-stubs-netsocket ...

Update netsocket and cellular unit tests to link with a mbed-stubs-netsocket
library that it depends on instead of link with mbed-stubs
which is a group of stubs libraries.