Unit tests: Move cmsis target_h stubs

This creates a new mbed-headers-cmsis which is always and only used
by mbed-headers-platform, so we add the former to the laters' linked
targets.

cmsis/CMakeLists.txt

@@ -4,3 +4,6 @@
 add_subdirectory(CMSIS_5)
 add_subdirectory(device)
 
+if(CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME AND BUILD_TESTING)
+    add_subdirectory(tests/UNITTESTS/doubles)
+endif()

cmsis/tests/UNITTESTS/.mbedignore

@@ -0,0 +1 @@
+*

cmsis/tests/UNITTESTS/doubles/CMakeLists.txt

@@ -0,0 +1,9 @@
+# Copyright (c) 2021 Arm Limited. All rights reserved.
+# SPDX-License-Identifier: Apache-2.0
+
+add_library(mbed-headers-cmsis INTERFACE)
+
+target_include_directories(mbed-headers-cmsis
+    INTERFACE
+        .
+)

platform/tests/UNITTESTS/doubles/CMakeLists.txt

@@ -10,6 +10,10 @@ target_include_directories(mbed-headers-platform
         ${mbed-os_SOURCE_DIR}/platform/randlib/include/
         ${mbed-os_SOURCE_DIR}/platform/mbed-trace/include
 )
+target_link_libraries(mbed-headers-platform
+    INTERFACE
+        mbed-headers-cmsis
+)
 
 add_library(mbed-stubs-platform)
 target_sources(mbed-stubs-platform