[Ada] New gnatbind switch -k

[Ada] New gnatbind switch -k

This switch can be used to disable the effect of -F when using -n
explicitly or implicitly.

gcc/ada/

	* bindgen.adb (Gen_Elab_Calls): Check for Check_Elaboration_Flags.
	* bindusg.adb (Display): Add -k.
	* opt.ads (Check_Elaboration_Flags): New.
	* switch-b.adb (Scan_Binder_Switches): Add processing of -k.
	* doc/gnat_ugn/building_executable_programs_with_gnat.rst: Add
	documentation for -k and -K.
	* gnat_ugn.texi: Regenerate.