nr2.0: Fix IfLet pattern handling

nr2.0: Fix IfLet pattern handling

gcc/rust/ChangeLog:

	* resolve/rust-default-resolver.cc
	(DefaultResolver::visit_if_let_patterns): New function
	definition.
	(DefaultResolver::visit): New IfLetExpr visitor definition.
	* resolve/rust-default-resolver.h
	(DefaultResolver::visit_if_let_patterns): New function
	declaration.
	(DefaultResolver::visit): New IfLetExpr visitor declaration.
	* resolve/rust-late-name-resolver-2.0.cc (Late::visit): Remove
	IfLetExpr visitor definition.
	(Late::visit_if_let_patterns): New function definition.
	* resolve/rust-late-name-resolver-2.0.h (Late::visit): Remove
	IfLetExpr visitor declaration.
	(Late::visit_if_let_patterns): New function declaration.
	* resolve/rust-name-resolution-context.h (BindingSource::IfLet):
	New enumerator.

Signed-off-by: Owen Avery <powerboat9.gamer@gmail.com>