[NFC] Normalize some test 'main' signatures

There were 3 tests with 'int main(void)', and 6 with the return type on a different line. I'm about to send a patch for main in tests, and this NFC change is unrelated.

llvm-svn: 350770

libcxx/test/std/utilities/function.objects/bind/func.bind/func.bind.bind/nested.pass.cpp

@@ -42,8 +42,7 @@ struct plus_one
   }
 };
 
-int
-main()
+int main()
 {
     using std::placeholders::_1;