gccrs: Fixes some tests appearing with a moved variant

gccrs: Fixes some tests appearing with a moved variant

A variant being moved lead to a null being created and a segfault later
down the line.

gcc/rust/ChangeLog:

	* backend/rust-compile-expr.cc (CompileExpr::visit): Call getter
	instead of size function.
	* checks/errors/privacy/rust-privacy-reporter.cc (PrivacyReporter::visit):
	Only check privacy if the type is present.
	* hir/rust-ast-lower-stmt.cc (ASTLoweringStmt::visit): Use an optional.
	* hir/tree/rust-hir-generic-param.h: Assert type before getting it.
	* hir/tree/rust-hir-item.h: Assert pointers before dereference, fix
	has_type condition.
	* hir/tree/rust-hir-path.h: Add more assertions.
	* hir/tree/rust-hir-stmt.cc: Change constructor with optionals.
	* hir/tree/rust-hir-stmt.h: Use optionals over smart pointers to
	emphasize these fields might be missing.
	* hir/tree/rust-hir.cc (LetStmt::as_string): Use getters.
	* typecheck/rust-hir-type-check-expr.cc: Clone structures to prevent
	parent's fields from being nulled by the move operation.
	* typecheck/rust-hir-type-check-item.cc (TypeCheckItem::visit): Use
	optionals.
	* typecheck/rust-tyty.cc: Likewise.
	* typecheck/rust-tyty.h: Likewise.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>