gccrs: lint: Do not emit unused warnings for public items

gccrs: lint: Do not emit unused warnings for public items

gcc/rust/ChangeLog:

	* checks/lints/rust-lint-scan-deadcode.h: Do not report public items
	as dead code.

gcc/testsuite/ChangeLog:

	* rust/compile/issue-1031.rs: Remove extraneous dead code warnings.
	* rust/compile/issue-1289.rs: Likewise.
	* rust/compile/test_mod.rs: Likewise.
	* rust/compile/torture/raw_identifiers.rs: Likewise.
	* rust/compile/torture/raw_identifiers_keywords.rs: Likewise.
	* rust/compile/privacy7.rs: New test.