equeue: Enable use of stub from C++ ...

Add extern "C" to the equeue_stub declaration to avoid an error when a C
file implements the equeue_stub symbol (as we do in equeue_stub.c).

    Undefined symbols for architecture x86_64:
      "_equeue_stub", referenced from:
          Test_LoRaWANTimer_start_Test::TestBody() in Test_LoRaWANTimer.cpp.o
    ld: symbol(s) not found for architecture x86_64
    clang: error: linker command failed with exit code 1 (use -v to see invocation)

cmake: Avoid linking to gcov ...

Use the `--coverage` option instead of manually linking to gcov, as some
host platforms (like macOS, FreeBSD) don't have gcov by default and use
an llvm equivalent instead.

equeue: Add missing header guards ...

The header equeue_stub.h was missing header guards to enforce single
inclusion. Add some header guards.

CMake: Move events fakes into events double dir ...

Previously events fakes as part of UNITTESTS/fakes, this PR moves
events fakes to events double directory to make events stubs
to be self-contained.

CMake: unit-tests: Make events stub only depend on headers it uses ...

Previously the events stub library depended on `mbed-headers`, which
is a collection of all available headers in mbed-os. To make it easier
to separate the library, only depend on the headers we're using.

CMake: Move events stub headers to the events/tests/UNITTESTS/double dir ...

Move events stubs headers to the mbed-os/events/tests/UNITTESTS/double
directory and update double CMake to include stub headers

CMake: unit-tests: Move mbed-headers-events to the events directory ...

Move the header-only mbed-headers-events library the unit test stubs
depend on into the events component directory. This makes the events
stubs more self-contained and improves the composition of the library.

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

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

events-timing test should not need any LED1

Merge pull request #14828 from hazzlim/add-cmake-supports-psa-tests ...

CMake: Add CMake to mbed-psa greentea tests

CMake: Require TEST_SOURCES in greentea CMake file ...

Assumption that greentea test file is always named main.cpp is
incorrect. Updated mbed_greentea_add_test() macro to make TEST_SOURCES
parameter compulsory, which is used to specify greentea test
file(s). This allows tests to use C, or have a different name.
Therefore also updated all pre-existing greentea test CMake files to
explicity add main.cpp to TEST_SOURCES.

CMake: unit-tests: Make events UNITTESTS only depend on headers it uses ...

Previously the events unit tests depended on `mbed-headers`, which
is a collection of all available headers in mbed-os. To make it easier
to separate the library, only depend on the headers we're using.

CMake: Only build unit tests if Mbed OS is the current project ...

Typically when adding a unit test directory to a CMake project a check
will be used to ensure the subdirectory is added only if the following
are true:

* The BUILD_TESTING option is set to ON.
* The current CMake project is the top-level project.

The reason being, if a downstream project includes our project they
generally don't want to build our unit tests.

In mbed-os, we do correctly specify the above condition before adding
the central UNITTEST subdirectory, which fetches googletest and adds the
"stub" libraries the unit tests depend on. However, we only check if
CMAKE_CROSSCOMPILING is OFF (or undefined) before actually adding the
unit tests. This mismatched logic would lead to unexpected build
failures in various scenarios. One likely case could be: a downstream
project including mbed-os happens to set CMAKE_CROSSCOMPILING to
OFF/undefined for any reason (possibly to build its own unit tests).
mbed-os would go ahead and attempt to build its tests without fetching
googletest or adding the required stub targets.

To fix the issue replace the check for CMAKE_CROSSCOMPILING in the unit
tests with the same BUILD_TESTING idiom we use for adding the central
UNITTESTS subdirectory.

CMake: Remove all unittest.cmake script from test suite ...

- Remove redundant cmake script as already added the CMake configuration file
- Remove redundant empty_baseline as it is no longer needed with the help of CMake configuration file

CMake: Move CMAKE_CROSSCOMPILING check inside library CMake

CMake: Refactor event unittest cmake ...

- Added CMake configuration file into events unittests

CMake: Add add_subdirectory of unittests ...

- add every libraries unittest directory into respective CMake
  which allows to include unittest source into build based on
  MBED_BUILD_UNITTESTS flag

Update UserAllocatedEvent.h

Update Event.h

Update equeue.h

Update EventQueue.h

Update equeue.h

Update README.md

Update README.md

Update README.md

extend the event generation int

bigger equeue generation size and only increment when needed ...

to mitigate against generation clash

Merge pull request #13975 from adbridge/eventq ...

Update EventQueue API to use chrono times

Remove trailing space

Tweak events API update and update Greentea tests accordingly