Now I am quite sure.
I thoroughly checked.
Whenever I try to write #include or or even with " " the files are now shown in the pull down menu.
Also I searched the entire of my PC, even at "...Atmel\Atmel Toolchain\AVR8 GCC\Native\3.4.1061\avr8-gnu-toolchain\avr\lib" this path. There is no such file as turn.h or follow-segment.h on my PC.
Also I checked the files "libpololu_*.a" and they are all available at this path: "Program Files\Atmel\Atmel Toolchain\AVR8 GCC\Native\3.4.1061\avr8-gnu-toolchain\avr\lib"
I am confused.