Ignore feature-gate-nll.rs in Polonius compare mode

This is a test about turning the NLL feature gate on, ignored by the NLL compare-mode.

src/test/ui/feature-gates/feature-gate-nll.rs

@@ -3,6 +3,7 @@
 
 // Don't use compare-mode=nll, since that turns on NLL.
 // ignore-compare-mode-nll
+// ignore-compare-mode-polonius
 
 #![feature(rustc_attrs)]
 

src/test/ui/feature-gates/feature-gate-nll.stderr

@@ -1,5 +1,5 @@
 warning[E0502]: cannot borrow `*x.1` as immutable because it is also borrowed as mutable
-  --> $DIR/feature-gate-nll.rs:14:13
+  --> $DIR/feature-gate-nll.rs:15:13
    |
 LL |     let m = &mut x;
    |             ------ mutable borrow occurs here
@@ -14,7 +14,7 @@ LL |     m;
    = note: for more information, try `rustc --explain E0729`
 
 error: compilation successful
-  --> $DIR/feature-gate-nll.rs:10:1
+  --> $DIR/feature-gate-nll.rs:11:1
    |
 LL | / fn main() {
 LL | |     let mut x = (33, &0);