gccrs: v0-mangle closures

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::generate_closure_function):
	Fix reference to node.
	* backend/rust-mangle.cc (struct V0Path): Modified to accept closures.
	(v0_crate_path): Modified to accept closures.
	(v0_closure): New function to mangle closures.
	(v0_path): Modified to accept closures
	* util/rust-mapping-common.h (UNKNOWN_NODEID): Change to UINT32_MAX.
	(UNKNOWN_HIRID): Change to UINT32_MAX.

gcc/testsuite/ChangeLog:

	* rust/compile/v0-mangle2.rs: New test.

Signed-off-by: Raiki Tamura <tamaron1203@gmail.com>