Add a test for rust-lang#26577

Author: varkor

src/test/ui/block-expression-remove-semicolon.rs

@@ -0,0 +1,10 @@
+fn foo() -> i32 {
+   0
+}
+
+fn main() {
+    let x: i32 = {
+        //~^ ERROR mismatched types
+        foo(); //~ HELP consider removing this semicolon
+    };
+}

src/test/ui/block-expression-remove-semicolon.stderr

@@ -0,0 +1,17 @@
+error[E0308]: mismatched types
+  --> $DIR/block-expression-remove-semicolon.rs:6:18
+   |
+LL |       let x: i32 = {
+   |  __________________^
+LL | |         //~^ ERROR mismatched types
+LL | |         foo(); //~ HELP consider removing this semicolon
+   | |              - help: consider removing this semicolon
+LL | |     };
+   | |_____^ expected i32, found ()
+   |
+   = note: expected type `i32`
+              found type `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.