Replace more DEBUG_EXPR_DECL creations with build_debug_expr_decl

Replace more DEBUG_EXPR_DECL creations with build_debug_expr_decl

As discussed on the mailing list, this patch replaces all but one
remaining open coded constructions of DEBUG_EXPR_DECL with calls to
build_debug_expr_decl, even if - in order not to introduce any
functional change - the mode of the constructed decl is then
overwritten.

It is not clear if changing the mode has any effect in practice and
therefore I have added a FIXME note to code which does it, as
requested.

After this patch, DEBUG_EXPR_DECLs are created only by
build_debug_expr_decl and make_debug_expr_from_rtl which looks like
it should be left alone.

gcc/ChangeLog:

2021-11-11  Martin Jambor  <mjambor@suse.cz>

	* cfgexpand.c (expand_gimple_basic_block): Use build_debug_expr_decl,
	add a fixme note about the mode assignment perhaps being unnecessary.
	* ipa-param-manipulation.c (ipa_param_adjustments::modify_call):
	Likewise.
	(ipa_param_body_adjustments::mark_dead_statements): Likewise.
	(ipa_param_body_adjustments::reset_debug_stmts): Likewise.
	* tree-inline.c (remap_ssa_name): Likewise.
	(tree_function_versioning): Likewise.
	* tree-into-ssa.c (rewrite_debug_stmt_uses): Likewise.
	* tree-ssa-loop-ivopts.c (remove_unused_ivs): Likewise.
	* tree-ssa.c (insert_debug_temp_for_var_def): Likewise.