This decouples -gnatRj from the destination, either standard output or file,
so that it only toggles the format of the representation information.

2018-05-29  Eric Botcazou  <ebotcazou@adacore.com>

gcc/ada/

	* doc/gnat_ugn/building_executable_programs_with_gnat.rst (Debugging
	Control): Adjust description of -gnatRj.
	* gnat_ugn.texi: Regenerate.
	* opt.ads (List_Representation_Info_To_JSON): Likewise.
	* repinfo.adb (List_Rep_Info): Do not automatically create a file
	if List_Representation_Info_To_JSON is true.
	* switch-c.adb (Scan_Front_End_Switches) <R>: Remove incompatibility
	check between -gnatRj and -gnatRs.
	* usage.adb (Usage): Adjust description of -gnatRj.

From-SVN: r260873