Use CPP defines for default x86 and x86_64 ISA features

We were previously getting a lot of warnings about mismatched
instruction set features when running on x86 architectures. Example
warning:

    Mismatch between dex2oat instruction set features to use

This change uses the CPP defines to get the default features in this
case so the mismatch will not be present anymore.

Bug: 155324337
Test: run a Golem benchmark (e.g. LU), observe that warning is missing.
Test: m test-art-host-gtest
Change-Id: I07d6a25094830d8d50fd451959e8dfd310262471
3 files changed