cmake - preprocess entire project and store output in file

i have a huge arm-none-eabi (gcc) cmake project.

i would like to run the entire project and abort after the preprocessor.

so example:

if i have 500 headers and 600 source files, i would like to get 1100 additional files after the preprocessor, all in a preprocessed state.

eg

// my procject

main.cpp
src/dummy.cpp
src/etc.cpp
... 

// my project after preprocessor

main.cpp
main_preprocessed.cpp
src/dummy.cpp
src/dummy_preprocessed.cpp
...

if i just add the compiler flag -E, the prepocessing happens and thells me 'linker input file unused because linking not done'. which is ok, but i dont get the preprocessed files.

just preprocessing one file is no good to me because i would need to add a lot of header files with -I, which takes a long time.

ADDITIONAL INFO:

also, what is important is that i need my project files preprocessed. additionally to my project files i do have some libraries from different manufacturers, those i build first into a static lib, then link against the lib.