enable clflushopt_target_feature in core's lib.rs

Author: folkertdev

library/core/src/lib.rs

@@ -181,6 +181,7 @@
 #![feature(aarch64_unstable_target_feature)]
 #![feature(arm_target_feature)]
 #![feature(avx10_target_feature)]
+#![feature(clflushopt_target_feature)]
 #![feature(hexagon_target_feature)]
 #![feature(loongarch_target_feature)]
 #![feature(mips_target_feature)]