Avoid mutation target collisions when embedded

CMakeLists.txt

@@ -99,9 +99,16 @@ set_tests_properties(
 # notices. This is a meta-check on the tests themselves, so it is a manual
 # target (it rebuilds and re-runs the whole suite many times), not a CTest test.
 #   cmake --build build --target mutation
+# When embedded in another project, use a namespaced target to avoid collisions
+# with mutation targets provided by sibling dependencies.
 find_package(Python3 COMPONENTS Interpreter)
 if(Python3_FOUND)
-    add_custom_target(mutation
+    if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+        set(AKERR_MUTATION_TARGET mutation)
+    else()
+        set(AKERR_MUTATION_TARGET akerror_mutation)
+    endif()
+    add_custom_target(${AKERR_MUTATION_TARGET}
         COMMAND ${Python3_EXECUTABLE}
                 ${CMAKE_CURRENT_SOURCE_DIR}/scripts/mutation_test.py
                 --source-root ${CMAKE_CURRENT_SOURCE_DIR}