A few notes: You can use, eg., the file command to check if executables are stripped. (with something like "file /bin/executable") But gdb already tells you that no debugging symbols were found for the executable. Thus, you either need install an lxrandr package with debugging symbols (with -g and unstripped), or (if you splitted out the debugging symbols during the build) install lxrandr together with its split debugging symbols.
