This is a reland of 313d4844
which was a reland of 0a59e0cb
which was a reland of 146f5375
which was a reland of d91679bf

Manually zero out flags with memset, since GCC appears not to initialize
the bitfield values to zero even with a default constructor.

Original change's description:
> [parser] Introduce UnoptimizedCompileFlags
>
> UnoptimizedCompileFlags defines the input flags shared between parse and
> compile (currently parse-only). It is set initially with some values, and
> is immutable after being passed to ParseInfo (ParseInfo still has getters
> for the fields, but no setters).
>
> Since a few of the existing flags were output flags, ParseInfo now has a
> new output_flags field, which will eventually migrate to a ParseOutputs
> structure.
>
> Bug: v8:10314
> Change-Id: If3890a5fad883bca80a97bf9dfe44d91797dc286
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2096580
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
> Reviewed-by: Simon Zünd <szuend@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#66782}

TBR=ulan@chromium.org,szuend@chromium.org,rmcilroy@chromium.org

Bug: v8:10314
Change-Id: I23bd6f9f14e9d0bbdde91aad46be1a646fd9647d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2157372Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67271}