Add tests for resolution changes

src/test/ui/resolve/crate-called-as-function.rs

@@ -0,0 +1,3 @@
+fn main() {
+    ::foo() //~ cannot find external crate `foo` in the crate root
+}

src/test/ui/resolve/crate-called-as-function.stderr

@@ -0,0 +1,9 @@
+error[E0425]: cannot find external crate `foo` in the crate root
+  --> $DIR/crate-called-as-function.rs:2:7
+   |
+LL |     ::foo()
+   |       ^^^ not found in the crate root
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0425`.

src/test/ui/resolve/missing-in-namespace.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let _map = std::hahmap::HashMap::new();
+    //~^ ERROR failed to resolve: could not find `hahmap` in `std
+}

src/test/ui/resolve/missing-in-namespace.stderr

@@ -0,0 +1,14 @@
+error[E0433]: failed to resolve: could not find `hahmap` in `std`
+  --> $DIR/missing-in-namespace.rs:2:29
+   |
+LL |     let _map = std::hahmap::HashMap::new();
+   |                             ^^^^^^^ not found in `std::hahmap`
+   |
+help: consider importing this struct
+   |
+LL | use std::collections::HashMap;
+   |
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0433`.