Update CMakeLists.txt

Author: jcbhmr

CMakeLists.txt

@@ -67,7 +67,7 @@ set(CPACK_PACKAGE_FILE_NAME "${PROJECT_NAME}-${CMAKE_SYSTEM_NAME}-${CMAKE_SYSTEM
 include(CPack)
 
 # Tasks
-if(BUILD_TESTING)
+if(BUILD_TESTING AND CMAKE_SOURCE_DIR STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
   file(
     GLOB_RECURSE
     c_cxx_files