In order to accomodate the debugger's support evolution for "new" DWARF
constructs, we need to have an flag that controls the amount of GNAT
encodings/standard DWARF information that is emitted in the debug info.
Propagate this new parameter into the Ada front-end.

gcc/ChangeLog:

	* common.opt (gnat_encodings): New variable
	(dwarf_gnat_encodings): New enum type.
	(fgnat_encodings): New option.
	* flag-types.h (enum dwarf_gnat_encodings): New.

gcc/ada/ChangeLog:

	* gcc-interface/misc.c (gnat_encodings): Undefine macro and
	declare a global variable.
	(gnat_post_options): Initialize this global from options.

From-SVN: r231761