[LLVM][X86][Goldmont] Adding new target-cpu: Goldmont

[LLVM SIDE]
Connecting the GoldMont processor to his feature.

Reviewers: 
1. igorb
2. zvi
3. delena
4. RKSimon
5. craig.topper        

Differential Revision: https://reviews.llvm.org/D34504

llvm-svn: 306658