Use Cargo.toml lints instead of a build script

Author: sayantn

crates/core_arch/Cargo.toml

@@ -26,3 +26,6 @@ std_detect = { version = "0.*", path = "../std_detect" }
 
 [target.'cfg(all(target_arch = "x86_64", target_os = "linux"))'.dev-dependencies]
 syscalls = { version = "0.6.18", default-features = false }
+
+[lints.rust]
+unexpected_cfgs = {level = "warn", check-cfg = ['cfg(stdarch_intel_sde)'] }