gccrs: Fix missing dead code analysis ICE on local enum definition

gccrs: Fix missing dead code analysis ICE on local enum definition

When resolving local enum's within a Block the name resolution info is
not at the top of the stack so this patch introduces a new mappings class
for miscellaneous name resolutions which can be used during path analaysis.

Fixes #1272

gcc/rust/ChangeLog:

	* resolve/rust-name-resolver.h: Add miscellenaous item mappings.
	* resolve/rust-name-resolver.cc (Resolver::insert_resolved_misc): Use
	new mappings.
	(Resolver::lookup_resolved_misc): Likewise.
	* typecheck/rust-hir-type-check-path.cc (TypeCheckExpr::resolve_segments):
	Adapt function to insert into miscelleanous mappings.
	* checks/lints/rust-lint-marklive.cc (MarkLive::find_ref_node_id):
	Allow lookup in miscelleanous mappings in mark-live phase.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1272.rs: New test.