Spurious floattidf failures on mips

[alexcrichton]

This was coming up every so often on #166 so wanted to jot this down before I forgot.

---- floattidf stdout ----

	thread 'floattidf' panicked at 'assertion failed: `(left == right)`

  left: `((-56294995342131100,), 14335762557005848176, 14335762557005848160, true)`,

 right: `((-56294995342131100,), 14335762557005848176, 14335762557005848160, false)`', /target/mips-unknown-linux-gnu/debug/build/compiler_builtins-7252d96c089bca74/out/floattidf.rs:10055

[est31]

Yup, I've got this in #161 as well, but lacked the discipline to open an issue :)

[mattico]

Here's the test:

static TEST_CASES: &[((i128,), u64)] = &[ /*...*/ ];

#[test]
fn floattidf() {
    for &((a,), b) in TEST_CASES {
        let b_ = __floattidf(a);
        let g_b = to_u64(b_);
        let diff = if g_b > b { g_b - b } else { b - g_b };
        assert_eq!(((a,), b, g_b, true), ((a,), b, g_b, diff <= 1));
    }
}

[AaronKutch]

This has been fixed by #397