project
|------ CMakeLists.txt (The main Cmake)
|------ ProjectA
|          |----- src
                   |.c files
|          |----- include
                   |.h files
|          |----- CMakeList.txt
|------ ProjectB
|          |----- src
                   |.c files
|          |----- include
                   |.h files
|          |----- CMakeList.txt
|
|------ build
|         |-----  ...
|------ bin
|        |---- executables

#cmake output directory
...
#compiler
...
set(CMAKE_C_FLAGS "... -DDEBUG ...")
#Linking
...
#add executables
...

add_subdirectory(ProjectA)
add_subdirectory(ProjectB)