Port e82b7ccd

Original Commit Message:

    I originally needed this for the initialization of a constexpr array in
    the wasm lazy compile builtin, but since it's a bigger change, I now
    split it off as this separate CL.
    The style guide recommends constexpr over const. I thus apply the
    constexprificaton over all headers that I touched anyway.

    I also remove the ARM64_DEFINE_REG_STATICS hack. It was introduced when
    merging in arm64 support more than three years ago, and I don't see the
    purpose for this.
    Also, some #defines can now be constexpr definitions, which was not
    possible before according to the comment.

R=clemensh@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2733323003
Cr-Commit-Position: refs/heads/master@{#43678}