Rollup merge of #22747 - krdln:fix-parsing-minus, r=alexcrichton

Makes Rust less amusing by fixing [#22745](https://github.com/rust-lang/rust/issues/22745)

src/libcore/num/mod.rs

@@ -1672,6 +1672,7 @@ macro_rules! from_str_radix_int_impl {
                 let is_signed_ty = (0 as $T) > Int::min_value();
 
                 match src.slice_shift_char() {
+                    Some(('-', "")) => Err(PIE { kind: Empty }),
                     Some(('-', src)) if is_signed_ty => {
                         // The number is negative
                         let mut result = 0;

src/libcoretest/num/mod.rs

@@ -122,4 +122,9 @@ mod test {
         assert_eq!("-9223372036854775808".parse::<i64>().ok(), Some(i64_val));
         assert_eq!("-9223372036854775809".parse::<i64>().ok(), None);
     }
+
+    #[test]
+    fn test_int_from_minus_sign() {
+        assert_eq!("-".parse::<i32>().ok(), None);
+    }
 }