Changed Opts.EABIVersion type string to llvm::EABI enum class

Summary:
Changed EABIVersion type from string to llvm::EABI.
It seems it was just a typo and this is intended implementation.

Differential Revision: https://reviews.llvm.org/D34595

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@306953 91177308-0d34-0410-b5e6-96231b3b80d8