CMake: pass application name to post-build hook

Pass the exact name to the post-build hook, when an application's
or test's `CMakeLists.txt` calls `mbed_set_post_build()`. The
interface is CMake's built-in mechanism:
* `set_target_properties()` to set a property, e.g. application name
* `$<TARGET_PROPERTY:target,property>` to query a property at run time

CMakeLists.txt

@@ -177,6 +177,12 @@ function(mbed_generate_bin_hex target)
         # through the post-build process once.
         file(REMOVE ${CMAKE_CURRENT_BINARY_DIR}/${target}.elf)
 
+        # Pass the application's name to the Mbed target's post build operation
+        set_target_properties(mbed-post-build-bin-${MBED_TARGET}
+            PROPERTIES
+                application ${target}
+        )
+
         # The artefacts must be created before they can be further manipulated
         add_dependencies(mbed-post-build-bin-${MBED_TARGET} ${target})