If I set in  my .emacs file: 
(setq LaTeX-includegraphics-read-file `LaTeX-includegraphics-read-file-TeX)
I get the following problem with C-c C-m includegraphics: After asking for the options it hangs and after a minute or so, it displays the error message: 

TeX-search-files: Variable binding depth exceeds max-specpdl-size

I used setenv to try several variants for TEXINPUTS, but always with the same result (also if I leave the TEXINPUTS variable empty).

Auctex version: 11.90.2.2017-07-25
TexLive Version 2015.20160320-1ubuntu0.1 (on ubuntu 16.04)