Declares __cpu_model as dso local

Declares __cpu_model as dso local

__builtin_cpu_supports and __builtin_cpu_is use information in __cpu_model to decide cpu features. Before this change, __cpu_model was not declared as dso local. The generated code looks up the address in GOT when reading __cpu_model. This makes it impossible to use these functions in ifunc, because at that time GOT entries have not been relocated. This change makes it dso local.

Differential Revision: https://reviews.llvm.org/D53850

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@348978 91177308-0d34-0410-b5e6-96231b3b80d8