[X86] Add RDRAND feature to GLM CPU

[craig.topper]

Summary

I believe this should be supported on GLM since RDSEED is.

[RKSimon]

LGTM, we're already saying that Goldmont supports rdrand in clang. Up to you if you want to add goldmont tests to the rdrand.ll/rdseed.ll tests (we haven't bothered for any other cpus).

lib/Target/X86/X86.td

class GoldmontProc<string Name> : ProcessorModel<Name, SLMModel, [
   FeaturePRFCHW,
   FeatureCallRegIndirect,
   FeatureSlowLEA,
   FeatureSlowIncDec,
   FeatureSlowBTMem,
   FeatureLAHFSAHF,
   FeatureMPX,
   FeatureSHA,
+  FeatureRDRAND,
   FeatureRDSEED,
   FeatureXSAVE,
   FeatureXSAVEOPT,
   FeatureXSAVEC,
   FeatureXSAVES,
   FeatureCLFLUSHOPT
 ]>;
 def : GoldmontProc<"goldmont">;