Add a disclaimer about x86 `f128` math functions · patricklam/verify-rust-std@e844eff

Original file line number	Diff line number	Diff line change
`@@ -1244,6 +1244,9 @@ mod prim_f64 {}`
`1244`	`1244`	`/// actually implement it. For x86-64 and AArch64, ISA support is not even specified,`
`1245`	`1245`	/// so it will always be a software implementation significantly slower than `f64`.
`1246`	`1246`	`///`
	`1247`	+/// _Note: `f128` support is incomplete. Many platforms will not be able to link math functions. On
	`1248`	`+/// x86 in particular, these functions do link but their results are always incorrect._`
	`1249`	`+///`
`1247`	`1250`	/// [See also the `std::f128::consts` module](crate::f128::consts).
`1248`	`1251`	`///`
`1249`	`1252`	`/// [wikipedia]: https://en.wikipedia.org/wiki/Quadruple-precision_floating-point_format`