Enable unexpected cfgs lint (#656)

Previously, the only way to configure this lint was using a build.rs
file, but now it can be done using Cargo.toml as well.

curve25519-dalek/Cargo.toml

@@ -71,3 +71,13 @@ group-bits = ["group", "ff/bits"]
 
 [target.'cfg(all(not(curve25519_dalek_backend = "fiat"), not(curve25519_dalek_backend = "serial"), target_arch = "x86_64"))'.dependencies]
 curve25519-dalek-derive = { version = "0.1", path = "../curve25519-dalek-derive" }
+
+[lints.rust.unexpected_cfgs]
+level = "warn"
+check-cfg = [
+    'cfg(allow_unused_unsafe)',
+    'cfg(curve25519_dalek_backend, values("fiat", "serial", "simd"))',
+    'cfg(curve25519_dalek_diagnostics, values("build"))',
+    'cfg(curve25519_dalek_bits, values("32", "64"))',
+    'cfg(nightly)',
+]

curve25519-dalek/src/backend/vector/ifma/edwards.rs

@@ -249,7 +249,7 @@ impl<'a> From<&'a edwards::EdwardsPoint> for NafLookupTable8<CachedPoint> {
     }
 }
 
-#[cfg(target_feature = "avx512ifma,avx512vl")]
+#[cfg(all(target_feature = "avx512ifma", target_feature = "avx512vl"))]
 #[cfg(test)]
 mod test {
     use super::*;

curve25519-dalek/src/backend/vector/ifma/field.rs

@@ -629,7 +629,7 @@ impl<'a, 'b> Mul<&'b F51x4Reduced> for &'a F51x4Reduced {
     }
 }
 
-#[cfg(target_feature = "avx512ifma,avx512vl")]
+#[cfg(all(target_feature = "avx512ifma", target_feature = "avx512vl"))]
 #[cfg(test)]
 mod test {
     use super::*;

curve25519-dalek/src/lib.rs

@@ -42,8 +42,6 @@
     unused_lifetimes,
     unused_qualifications
 )]
-// Requires MSRV 1.77 as it does not allow build.rs gating
-#![allow(unexpected_cfgs)]
 
 //------------------------------------------------------------------------
 // External dependencies: