Fix type (exit → exist)

Author: tbu-

tests/ui/rfcs/rfc-2627-raw-dylib/invalid-dlltool.rs

@@ -1,7 +1,7 @@
 // Tests that failing to run dlltool will raise an error.
 
 //@ needs-dlltool
-//@ compile-flags: --crate-type lib --emit link -Cdlltool=does_not_exit.exe
+//@ compile-flags: --crate-type lib --emit link -Cdlltool=does_not_exist.exe
 #[link(name = "foo", kind = "raw-dylib")]
 extern "C" {
     fn f(x: i32);