Introduce instance discriminators

Introduce instance discriminators

With -gnateS, the Ada compiler sets itself up to output discriminators
for different instantiations of generics, but the middle and back ends
have lacked support for that.  This patch introduces the missing bits,
translating the GNAT-internal representation of the per-file instance
map to an instance_table that maps decls to instance discriminators.

From: Alexandre Oliva  <oliva@adacore.com>, Olivier Hainque  <hainque@adacore.com>
for  gcc/ChangeLog

	* debug.h (decl_to_instance_map_t): New type.
	(decl_to_instance_map): Declare.
	(maybe_create_decl_to_instance_map): New inline function.
    	* final.c (bb_discriminator, last_bb_discriminator): New statics,
    	to track basic block discriminators.
    	(final_start_function_1): Initialize them.
    	(final_scan_insn_1): On NOTE_INSN_BASIC_BLOCK, track
	bb_discriminator.
	(decl_to_instance_map): New variable.
	(map_decl_to_instance, maybe_set_discriminator): New functions.
    	(notice_source_line): Set discriminator.

for  gcc/ada/ChangeLog

	* trans.c: Include debug.h.
	(file_map): New static variable.
	(gigi): Set it.  Create decl_to_instance_map when needed.
	(Subprogram_Body_to_gnu): Pass gnu_subprog_decl to...
	(Sloc_to_locus): ... this.  Add decl parm, map it to instance.
	* gigi.h (Sloc_to_locus): Adjust declaration.

for  gcc/testsuite/ChangeLog

	* gnat.dg/dinst.adb: New.
	* gnat.dg/dinst_pkg.ads, gnat.dg/dinst_pkg.adb: New.

Co-Authored-By: Olivier Hainque <hainque@adacore.com>
From-SVN: r263182