Add a new precision adjustment for i586 exp2f

There was a recent failure from the random tests:

     ---- mp_random_exp2f stdout ----
    Random Mpfr exp2f arg 1/1: 10000 iterations (10000 total) using `LIBM_SEED=fqgMuzs6eqH1VZSEmQpLnThnaIyRUOWe`

    thread 'mp_random_exp2f' panicked at crates/libm-test/tests/multiprecision.rs:41:49:
    called `Result::unwrap()` on an `Err` value:
        input:    (127.97238,) (0x42fff1dc,)
        expected: 3.3383009e38           0x7f7b2556
        actual:   inf                    0x7f800000

    Caused by:
        mismatched infinities

Add an xfail for mismatched infinities on i586.

library/compiler-builtins/libm/crates/libm-test/src/precision.rs

@@ -211,6 +211,15 @@ impl MaybeOverride<(f32,)> for SpecialCase {
             return XFAIL;
         }
 
+        if cfg!(x86_no_sse)
+            && ctx.base_name == BaseName::Exp2
+            && !expected.is_infinite()
+            && actual.is_infinite()
+        {
+            // We return infinity when there is a representable value. Test input: 127.97238
+            return XFAIL;
+        }
+
         maybe_check_nan_bits(actual, expected, ctx)
     }