CMake: Refactor post-build hook to remove APP_TARGET references

There should not be a reference to APP_TARGET in Mbed OS as end-users
may decide to use a different name for the CMake variable to store their
application name.

CMakeLists.txt

@@ -187,11 +187,13 @@ function(mbed_generate_bin_hex target)
     )
 
     if(TARGET mbed-post-build-bin-${MBED_TARGET})
-        add_custom_target(mbed-post-build
-            ALL
-            DEPENDS
-                mbed-post-build-bin-${MBED_TARGET}
-        )
+        # The artefacts must be created before they can be further manipulated
+        add_dependencies(mbed-post-build-bin-${MBED_TARGET} ${target})
+
+        # Add a post-build hook to the top-level CMake target in the form of a
+        # CMake custom target. The hook depends on Mbed target specific
+        # post-build CMake target which has a custom command attached to it.
+        add_custom_target(mbed-post-build ALL DEPENDS mbed-post-build-bin-${MBED_TARGET})
     endif()
 endfunction()
 

tools/cmake/mbed_set_post_build.cmake

@@ -6,16 +6,11 @@
 #
 macro(mbed_set_post_build_operation)
 
-    add_custom_target(mbed-post-build-bin-${mbed_target_name}
-        DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${APP_TARGET}.bin
-    )
-
-    # Ensures the application artefacts are created before manipulating them.
-    add_dependencies(mbed-post-build-bin-${mbed_target_name} ${APP_TARGET})
+    add_custom_target(mbed-post-build-bin-${mbed_target_name})
 
     add_custom_command(
-        OUTPUT
-        ${CMAKE_CURRENT_BINARY_DIR}/${APP_TARGET}.bin
+        TARGET
+            mbed-post-build-bin-${mbed_target_name}
         POST_BUILD
         COMMAND
             ${post_build_command}