Added expected (compile-time) outputs.

* In the case of `derive-same-struct`, it seemed cleaner to add the
  output than to try to modify the macro itself (which is where the
  output is coming from).

* In the case of `custom-derive-partial-eq`, it was just easier to add
  the output than to attempt to port the test to use a procedural
  macro.

src/test/run-pass-fulldeps/custom-derive-partial-eq.stderr

@@ -0,0 +1,6 @@
+warning: `#[derive]` for custom traits is deprecated and will be removed in the future. Prefer using procedural macro custom derive.
+  --> $DIR/custom-derive-partial-eq.rs:17:10
+   |
+LL | #[derive(CustomPartialEq)] // Check that this is not a stability error.
+   |          ^^^^^^^^^^^^^^^
+

src/test/run-pass-fulldeps/proc-macro/derive-same-struct.stdout

@@ -0,0 +1 @@
+input1: "struct A;"