testsuite: Un-xfail unit-like-struct-drop-run on Windows

Closes #7999

Author: catamorphism

src/test/run-pass/unit-like-struct-drop-run.rs

@@ -9,7 +9,6 @@
 // except according to those terms.
 
 // Make sure the destructor is run for unit-like structs.
-// xfail-fast
 
 use std::task;
 
@@ -21,7 +20,7 @@ impl Drop for Foo {
     }
 }
 
-fn main() {
+pub fn main() {
     let x = do task::try {
         let _b = Foo;
     };