CMake: unit-tests: Move mbed-headers-platform to platform directory

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

UNITTESTS/stubs/CMakeLists.txt

@@ -4,7 +4,6 @@
 add_library(mbed-stubs-headers INTERFACE)
 add_library(mbed-headers INTERFACE)
 add_library(mbed-headers-base INTERFACE)
-add_library(mbed-headers-platform INTERFACE)
 add_library(mbed-headers-connectivity INTERFACE)
 add_library(mbed-headers-events INTERFACE)
 
@@ -19,15 +18,6 @@ target_link_libraries(mbed-headers
         mbed-headers-rtos
 )
 
-target_include_directories(mbed-headers-platform
-    INTERFACE
-        ${mbed-os_SOURCE_DIR}/platform/include
-        ${mbed-os_SOURCE_DIR}/platform/include/platform
-        ${mbed-os_SOURCE_DIR}/platform/randlib/include/mbed-client-randlib/
-        ${mbed-os_SOURCE_DIR}/platform/randlib/include/
-        ${mbed-os_SOURCE_DIR}/platform/mbed-trace/include
-)
-
 target_include_directories(mbed-headers-base
     INTERFACE
         ${mbed-os_SOURCE_DIR}/UNITTESTS/target_h

platform/tests/UNITTESTS/doubles/CMakeLists.txt

@@ -1,8 +1,17 @@
 # Copyright (c) 2021 ARM Limited. All rights reserved.
 # SPDX-License-Identifier: Apache-2.0
 
-add_library(mbed-stubs-platform)
+add_library(mbed-headers-platform INTERFACE)
+target_include_directories(mbed-headers-platform
+    INTERFACE
+        ${mbed-os_SOURCE_DIR}/platform/include
+        ${mbed-os_SOURCE_DIR}/platform/include/platform
+        ${mbed-os_SOURCE_DIR}/platform/randlib/include/mbed-client-randlib/
+        ${mbed-os_SOURCE_DIR}/platform/randlib/include/
+        ${mbed-os_SOURCE_DIR}/platform/mbed-trace/include
+)
 
+add_library(mbed-stubs-platform)
 target_sources(mbed-stubs-platform
     PRIVATE
         mbed_critical_stub.c
@@ -17,12 +26,10 @@ target_sources(mbed-stubs-platform
         randLIB_stub.c
         randLIB_stub.cpp
 )
-
 target_link_options(mbed-stubs-platform
     PRIVATE
         --coverage
 )
-
 target_link_libraries(mbed-stubs-platform
     PRIVATE
         mbed-headers