rdr: add incremental test exercising rustc_public_hash_changed and rustc_public_hash_unchanged attributes

Author: susitsm

tests/incremental/rdr/public_api_hash_attributes/auxiliary/dep.rs

@@ -0,0 +1,16 @@
+//@ [cpass_public_hash1]compile-flags: -Zpublic-api-hash
+//@ [cpass_public_hash2]compile-flags: -Zpublic-api-hash
+//@ [cpass_public_hash3]compile-flags: -Zpublic-api-hash
+
+#![crate_name = "dep"]
+#![crate_type = "rlib"]
+
+#[cfg(any(cpass1, cpass2))]
+pub fn generic<T: std::fmt::Debug>(v: T) {
+    panic!("{v:?}");
+}
+
+#[cfg(any(cpass3))]
+pub fn generic<T: std::fmt::Debug>(v: T) {
+    panic!("{v:?}");
+}

tests/incremental/rdr/public_api_hash_attributes/main.rs

@@ -0,0 +1,15 @@
+//@ revisions: cpass1 cpass2 cpass3
+//@ compile-flags: -Z query-dep-graph -Z public-api-hash
+//@ aux-build: dep.rs
+//@ ignore-backends: gcc
+
+#![feature(rustc_attrs)]
+#![crate_type = "bin"]
+#![rustc_public_hash_unchanged(crate_name = "dep", cfg = "cpass2")]
+#![rustc_public_hash_changed(crate_name = "dep", cfg = "cpass3")]
+
+extern crate dep;
+
+fn main() {
+    dep::generic::<u32>(1);
+}