Get Polonius borrow check to work in simple cases

* Restores the generation of outlives facts from subtyping.
* Restore liveness facts.
* Generate invalidates facts at the start point of each location,
  where we check for errors.
* Add a small test for simple cases.

src/test/ui/nll/polonius-smoke-test.rs

@@ -0,0 +1,47 @@
+// Check that Polonius borrow check works for simple cases.
+// ignore-compare-mode-nll
+// compile-flags: -Z borrowck=mir -Zpolonius
+
+pub fn return_ref_to_local() -> &'static i32 {
+    let x = 0;
+    &x //~ ERROR
+}
+
+pub fn use_while_mut() {
+    let mut x = 0;
+    let y = &mut x;
+    let z = x; //~ ERROR
+    let w = y;
+}
+
+pub fn use_while_mut_fr(x: &mut i32) -> &mut i32 {
+    let y = &mut *x;
+    let z = x; //~ ERROR
+    y
+}
+
+// Cases like this are why we have Polonius.
+pub fn position_dependent_outlives(x: &mut i32, cond: bool) -> &mut i32 {
+    let y = &mut *x;
+    if cond {
+        return y;
+    } else {
+        *x = 0;
+        return x;
+    }
+}
+
+fn foo<'a, 'b>(p: &'b &'a mut usize) -> &'b usize {
+    p
+}
+
+// Check that we create constraints for well-formedness of function arguments
+fn well_formed_function_inputs() {
+    let s = &mut 1;
+    let r = &mut *s;
+    let tmp = foo(&r);
+    s; //~ ERROR
+    tmp;
+}
+
+fn main() {}

src/test/ui/nll/polonius-smoke-test.stderr

@@ -0,0 +1,45 @@
+error[E0597]: `x` does not live long enough
+  --> $DIR/polonius-smoke-test.rs:7:5
+   |
+LL |     &x //~ ERROR
+   |     ^^ borrowed value does not live long enough
+LL | }
+   | - `x` dropped here while still borrowed
+   |
+   = note: borrowed value must be valid for the static lifetime...
+
+error[E0503]: cannot use `x` because it was mutably borrowed
+  --> $DIR/polonius-smoke-test.rs:13:13
+   |
+LL |     let y = &mut x;
+   |             ------ borrow of `x` occurs here
+LL |     let z = x; //~ ERROR
+   |             ^ use of borrowed `x`
+LL |     let w = y;
+   |             - borrow later used here
+
+error[E0505]: cannot move out of `x` because it is borrowed
+  --> $DIR/polonius-smoke-test.rs:19:13
+   |
+LL |     let y = &mut *x;
+   |             ------- borrow of `*x` occurs here
+LL |     let z = x; //~ ERROR
+   |             ^ move out of `x` occurs here
+LL |     y
+   |     - borrow later used here
+
+error[E0505]: cannot move out of `s` because it is borrowed
+  --> $DIR/polonius-smoke-test.rs:43:5
+   |
+LL |     let r = &mut *s;
+   |             ------- borrow of `*s` occurs here
+LL |     let tmp = foo(&r);
+LL |     s; //~ ERROR
+   |     ^ move out of `s` occurs here
+LL |     tmp;
+   |     --- borrow later used here
+
+error: aborting due to 4 previous errors
+
+Some errors occurred: E0503, E0505, E0597.
+For more information about an error, try `rustc --explain E0503`.