Add test with current behaviour.

This commit adds a test demonstrating the current behaviour when a macro
defined in a module with the `#[macro_export]` is imported from the
module rather than the crate root.

Author: davidtwco

src/test/ui/auxiliary/issue-59764.rs

@@ -0,0 +1,8 @@
+pub mod foo {
+    #[macro_export]
+    macro_rules! makro {
+        ($foo:ident) => {
+            fn $foo() { }
+        }
+    }
+}

src/test/ui/issue-59764.rs

@@ -0,0 +1,14 @@
+// aux-build:issue-59764.rs
+// compile-flags:--extern issue_59764
+// edition:2018
+
+use issue_59764::foo::makro;
+//~^ ERROR unresolved import `issue_59764::foo::makro` [E0432]
+
+makro!(bar);
+//~^ ERROR cannot determine resolution for the macro `makro`
+
+fn main() {
+    bar();
+    //~^ ERROR cannot find function `bar` in this scope [E0425]
+}

src/test/ui/issue-59764.stderr

@@ -0,0 +1,24 @@
+error[E0432]: unresolved import `issue_59764::foo::makro`
+  --> $DIR/issue-59764.rs:5:5
+   |
+LL | use issue_59764::foo::makro;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^ no `makro` in `foo`
+
+error: cannot determine resolution for the macro `makro`
+  --> $DIR/issue-59764.rs:8:1
+   |
+LL | makro!(bar);
+   | ^^^^^
+   |
+   = note: import resolution is stuck, try simplifying macro imports
+
+error[E0425]: cannot find function `bar` in this scope
+  --> $DIR/issue-59764.rs:12:5
+   |
+LL |     bar();
+   |     ^^^ not found in this scope
+
+error: aborting due to 3 previous errors
+
+Some errors occurred: E0425, E0432.
+For more information about an error, try `rustc --explain E0425`.