x86 target features: make pclmulqdq imply sse2

Author: RalfJung

compiler/rustc_target/src/target_features.rs

@@ -316,7 +316,7 @@ const X86_ALLOWED_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
 ("lahfsahf",Unstable(sym::lahfsahf_target_feature),&[]),
 ("lzcnt",Stable,&[]),
 ("movbe",Stable,&[]),
-("pclmulqdq",Stable,&[]),
+("pclmulqdq",Stable,&["sse2"]),
 ("popcnt",Stable,&[]),
 ("prfchw",Unstable(sym::prfchw_target_feature),&[]),
 ("rdrand",Stable,&[]),