ART: Add experimental constexpr

Add a constexpr flag to bypass a branch in the verifier when there
are no experimental dex instructions. Guarantee the value with
static_asserts.

Bug: 10921004
Test: m test-art-host
Change-Id: Ib77b6142c4d2debe4b4d4fec60c02d92b1e7349f
3 files changed