Regression in powi on Windows beta/nightly

[iliekturtles]

https://travis-ci.org/github/iliekturtles/uom/builds/698980459?utm_medium=notification&utm_source=email

extern crate typenum; // 2.12.0

fn main() {
    let v = 12.046623229980468750000000000000_f32;
    let a = a(v);
    let b = b(v);

    println!("std powi {:.30?}", a);
    println!("typenum  {:.30?}", b);
}

#[inline(never)]
fn a(v: f32) -> f32 {
    v.powi(3)
}

#[inline(never)]
fn b(v: f32) -> f32 {
    typenum::Pow::powi(v, typenum::P3::new())
}

/d/Code/Test/rust/tst (master)$ cargo run; rustc --version
   Compiling tst v0.1.0 (D:\Code\Test\rust\tst)
    Finished dev [unoptimized + debuginfo] target(s) in 3.90s
     Running `target\debug\tst.exe`
std powi 1748.219482421875000000000000000000
typenum  1748.219482421875000000000000000000
rustc 1.44.0 (49cae5576 2020-06-01)
/d/Code/Test/rust/tst (master)$ cargo +beta run; rustc +beta --version
    Finished dev [unoptimized + debuginfo] target(s) in 2.79s
     Running `target\debug\tst.exe`
std powi 1748.219604492187500000000000000000
typenum  1748.219482421875000000000000000000
rustc 1.45.0-beta.3359 (b7dc83a3f 2020-06-03)