Cleaned up some tests

Merged tests/ui/typeck/non-function-call-error-2 with
tests/ui/typeck/non-function-call-error

Add comment to
tests/ui/traits/normalize-associated-type-in-where-clause.rs

Merged tests/ui/privacy/private-item-simple-2.rs with
tests/ui/privacy/private-item-simple.rs

Merged tests/ui/str/str-add-operator-2.rs with
tests/ui/str/str-add-operator.rs

Add comment to tests/ui/imports/duplicate-empty-imports.rs

Add comment to tests/ui/for-loop-while/nested-loop-break-unit.rs

Add comment to tests/ui/match/match-ref-option-pattern.rs

Add comment to tests/ui/closures/simple-capture-and-call.rs

Add comment to tests/ui/type/never-type-inference-fail.rs

Add comment to tests/ui/match/match-stack-overflow-72933.rs

Author: reddevilmidzy

tests/ui/closures/simple-capture-and-call.rs

@@ -1,7 +1,8 @@
+//! regression test for issue #1895
 //@ run-pass
 
-pub fn main() {
-  let x = 1_usize;
-  let y = || x;
-  let _z = y();
+fn main() {
+    let x = 1_usize;
+    let y = || x;
+    let _z = y();
 }

tests/ui/for-loop-while/nested-loop-break-unit.rs

@@ -1,3 +1,4 @@
+//! regression test for issue #2642
 //@ run-pass
 #![allow(dead_code)]
 

tests/ui/imports/duplicate-empty-imports.rs

@@ -1,3 +1,4 @@
+//! regression test for issue #47673
 //@ check-pass
 #![allow(unused_imports)]
 

tests/ui/match/match-ref-option-pattern.rs

@@ -1,3 +1,4 @@
+//! regression test for issue #3500
 //@ run-pass
 
 pub fn main() {

tests/ui/match/match-stack-overflow-72933-.rs

@@ -1,6 +1,7 @@
+//! regression test for issue #72933
 //@ build-pass
 // ignore-tidy-filelength
-#![crate_type="rlib"]
+#![crate_type = "rlib"]
 
 fn banana(v: &str) -> u32 {
     match v {

tests/ui/privacy/private-item-simple-2.rs

@@ -1,7 +1,13 @@
+//! regression test for issue #3993
+
 mod a {
     fn f() {}
 }
 
 fn main() {
     a::f(); //~ ERROR function `f` is private
 }
+
+fn foo() {
+    use a::f; //~ ERROR function `f` is private
+}

tests/ui/privacy/private-item-simple-2.stderr

@@ -1,15 +1,27 @@
 error[E0603]: function `f` is private
-  --> $DIR/private-item-simple.rs:6:8
+  --> $DIR/private-item-simple.rs:12:12
+   |
+LL |     use a::f;
+   |            ^ private function
+   |
+note: the function `f` is defined here
+  --> $DIR/private-item-simple.rs:4:5
+   |
+LL |     fn f() {}
+   |     ^^^^^^
+
+error[E0603]: function `f` is private
+  --> $DIR/private-item-simple.rs:8:8
    |
 LL |     a::f();
    |        ^ private function
    |
 note: the function `f` is defined here
-  --> $DIR/private-item-simple.rs:2:5
+  --> $DIR/private-item-simple.rs:4:5
    |
 LL |     fn f() {}
    |     ^^^^^^
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0603`.