set(all_files 
${CMAKE_CURRENT_SOURCE_DIR}/src/csystem_external.h
${CMAKE_CURRENT_SOURCE_DIR}/src/csystem_external.cpp
)

set(inc_files ${all_files})
set(src_files ${all_files})
list(FILTER inc_files INCLUDE REGEX ".*.h$")
list(FILTER src_files INCLUDE REGEX ".*.cpp$")

source_group("cmake" REGULAR_EXPRESSION [.]*cmake[.]*)