Add core FreeRTOS files

libraries/FreeRTOS/inc/CMakeLists.txt

@@ -0,0 +1,15 @@
+# FreeRTOS internal cmake file. Do not use it in user top-level project
+
+add_library(freertos_kernel_include INTERFACE)
+
+target_include_directories(freertos_kernel_include
+    INTERFACE
+        .
+        # Note: DEPRECATED but still supported, may be removed in a future release.
+        $<$<NOT:$<TARGET_EXISTS:freertos_config>>:${FREERTOS_CONFIG_FILE_DIRECTORY}>
+)
+
+target_link_libraries(freertos_kernel_include
+    INTERFACE
+        $<$<TARGET_EXISTS:freertos_config>:freertos_config>
+)