Issue Description

Compiling librealsense as a static library with all options disabled will cause the compiler to error on the file src/linux/backend-hid.h/cpp (Logs included below)

It seems that the < fstream > dependency is not included in any of the headers. However, if you set BUILD_EASYLOGGINGPP to TRUE, the error will go away.

I've locally fixed this issue by including < fstream > in src/backend.h.

Maybe consider adding this or a similar change in the source.

Cmake options: https://imgur.com/a/yT1ezNl
make logs: https://pastebin.com/W9NB6s5W