Resolve unnecessary_transmutes lints

These appeared in a later nightly. In compiler-builtins we can apply the
suggestion, but in `libm` we need to ignore them since `fx::from_bits`
is not `const` at the MSRV.

`clippy::uninlined_format_args` also seems to have gotten stricter, so
fix those here.

library/compiler-builtins/libm/src/math/pow.rs

@@ -452,11 +452,7 @@ mod tests {
             } else {
                 pow(base, exponent) == expected
             },
-            "{} ** {} was {} instead of {}",
-            base,
-            exponent,
-            res,
-            expected
+            "{base} ** {exponent} was {res} instead of {expected}",
         );
     }
 
@@ -486,10 +482,7 @@ mod tests {
                     } else {
                         exp == res
                     },
-                    "test for {} was {} instead of {}",
-                    val,
-                    res,
-                    exp
+                    "test for {val} was {res} instead of {exp}",
                 );
             })
         });

library/compiler-builtins/libm/src/math/support/float_traits.rs

@@ -1,3 +1,5 @@
+#![allow(unknown_lints)] // FIXME(msrv) we shouldn't need this
+
 use core::{fmt, mem, ops};
 
 use super::int_traits::{CastFrom, Int, MinInt};
@@ -344,24 +346,28 @@ float_impl!(
 /* FIXME(msrv): vendor some things that are not const stable at our MSRV */
 
 /// `f32::from_bits`
+#[allow(unnecessary_transmutes)] // lint appears in newer versions of Rust
 pub const fn f32_from_bits(bits: u32) -> f32 {
     // SAFETY: POD cast with no preconditions
     unsafe { mem::transmute::<u32, f32>(bits) }
 }
 
 /// `f32::to_bits`
+#[allow(unnecessary_transmutes)] // lint appears in newer versions of Rust
 pub const fn f32_to_bits(x: f32) -> u32 {
     // SAFETY: POD cast with no preconditions
     unsafe { mem::transmute::<f32, u32>(x) }
 }
 
 /// `f64::from_bits`
+#[allow(unnecessary_transmutes)] // lint appears in newer versions of Rust
 pub const fn f64_from_bits(bits: u64) -> f64 {
     // SAFETY: POD cast with no preconditions
     unsafe { mem::transmute::<u64, f64>(bits) }
 }
 
 /// `f64::to_bits`
+#[allow(unnecessary_transmutes)] // lint appears in newer versions of Rust
 pub const fn f64_to_bits(x: f64) -> u64 {
     // SAFETY: POD cast with no preconditions
     unsafe { mem::transmute::<f64, u64>(x) }