Make some float methods unstable const fn

Some float methods are now `const fn` under the `const_float_methods` feature gate.

In order to support `min`, `max`, `abs` and `copysign`, the implementation of some intrinsics had to be moved from Miri to rustc_const_eval.

Author: eduardosm

src/intrinsics/mod.rs

@@ -145,20 +145,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.write_scalar(Scalar::from_bool(branch), dest)?;
             }
 
-            // Floating-point operations
-            "fabsf32" => {
-                let [f] = check_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f32()?;
-                // This is a "bitwise" operation, so there's no NaN non-determinism.
-                this.write_scalar(Scalar::from_f32(f.abs()), dest)?;
-            }
-            "fabsf64" => {
-                let [f] = check_arg_count(args)?;
-                let f = this.read_scalar(f)?.to_f64()?;
-                // This is a "bitwise" operation, so there's no NaN non-determinism.
-                this.write_scalar(Scalar::from_f64(f.abs()), dest)?;
-            }
-
             "floorf32" | "ceilf32" | "truncf32" | "roundf32" | "rintf32" => {
                 let [f] = check_arg_count(args)?;
                 let f = this.read_scalar(f)?.to_f32()?;
@@ -249,31 +235,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
                 this.write_scalar(res, dest)?;
             }
 
-            "minnumf32" | "maxnumf32" | "copysignf32" => {
-                let [a, b] = check_arg_count(args)?;
-                let a = this.read_scalar(a)?.to_f32()?;
-                let b = this.read_scalar(b)?.to_f32()?;
-                let res = match intrinsic_name {
-                    "minnumf32" => this.adjust_nan(a.min(b), &[a, b]),
-                    "maxnumf32" => this.adjust_nan(a.max(b), &[a, b]),
-                    "copysignf32" => a.copy_sign(b), // bitwise, no NaN adjustments
-                    _ => bug!(),
-                };
-                this.write_scalar(Scalar::from_f32(res), dest)?;
-            }
-            "minnumf64" | "maxnumf64" | "copysignf64" => {
-                let [a, b] = check_arg_count(args)?;
-                let a = this.read_scalar(a)?.to_f64()?;
-                let b = this.read_scalar(b)?.to_f64()?;
-                let res = match intrinsic_name {
-                    "minnumf64" => this.adjust_nan(a.min(b), &[a, b]),
-                    "maxnumf64" => this.adjust_nan(a.max(b), &[a, b]),
-                    "copysignf64" => a.copy_sign(b), // bitwise, no NaN adjustments
-                    _ => bug!(),
-                };
-                this.write_scalar(Scalar::from_f64(res), dest)?;
-            }
-
             "fmaf32" => {
                 let [a, b, c] = check_arg_count(args)?;
                 let a = this.read_scalar(a)?.to_f32()?;