title: Why would a CMake build not start build when header file changes
body: <p>Below is a small sample of the way I'm building my project. I have a list of headers and a list of source files, and pass them to add_executable. Sometimes after several incremental builds, I'm changing the header file but the build isn't doing anything. The status shows that each target is checked but no changes are seen. If I do a small modification in the CPP file, then the build is executed.</p>
  
  <p>What could be the cause of this?</p>
  
  <pre><code>list (APPEND ${PROJ_NAME}_SRC_HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/include/lua/lua_config.hpp)
  list (APPEND ${PROJ_NAME}_SRC_FILES ${CMAKE_CURRENT_SOURCE_DIR}/source/lua/lua_config.cpp)
  add_executable(${PROJ_NAME} ${${PROJ_NAME}_SRC_FILES} ${${PROJ_NAME}_SRC_HEADERS})
  
  </code></pre>
  
  <p>I'm using the 'Unix Makefiles' generator.</p>
  
  <p>I see that all my projects header files are not part of the generated <code>depend.cmake</code> file. I guess this is the root of the problem. All the header files from the other conan packages are there, but not the ones for the top level project.</p>