Add test for showing rmeta candidates in error

Author: camelid

src/test/ui/crate-loading/auxiliary/crateresolve2-1.rs

@@ -0,0 +1,5 @@
+// compile-flags:-C extra-filename=-1 --emit=metadata
+#![crate_name = "crateresolve2"]
+#![crate_type = "lib"]
+
+pub fn f() -> isize { 10 }

src/test/ui/crate-loading/auxiliary/crateresolve2-2.rs

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+// compile-flags:-C extra-filename=-2 --emit=metadata
+#![crate_name = "crateresolve2"]
+#![crate_type = "lib"]
+
+pub fn f() -> isize { 20 }

src/test/ui/crate-loading/auxiliary/crateresolve2-3.rs

@@ -0,0 +1,5 @@
+// compile-flags:-C extra-filename=-3 --emit=metadata
+#![crate_name = "crateresolve2"]
+#![crate_type = "lib"]
+
+pub fn f() -> isize { 30 }

src/test/ui/crate-loading/crateresolve2.rs

@@ -0,0 +1,11 @@
+// check-fail
+
+// aux-build:crateresolve2-1.rs
+// aux-build:crateresolve2-2.rs
+// aux-build:crateresolve2-3.rs
+
+extern crate crateresolve2;
+//~^ ERROR multiple matching crates for `crateresolve2`
+
+fn main() {
+}

src/test/ui/crate-loading/crateresolve2.stderr

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+error[E0464]: multiple matching crates for `crateresolve2`
+  --> $DIR/crateresolve2.rs:7:1
+   |
+LL | extern crate crateresolve2;
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: candidates:
+
+error: aborting due to previous error
+