This is a reland of 491d5a81

Original change's description:
> [builtins] Embed builtins into the binary
>
> This embeds code for off-heap-safe builtins into the binary. Actual
> execution of embedded code is not implemented yet.
>
> The embedded file has the following format:
>
> namespace v8 {
> namespace internal {
>
> namespace {
>
> V8_EMBEDDED_TEXT_HEADER(v8_embedded_blob_)
> __asm__( /* builtin offsets and lengths */ );
> __asm__(V8_ASM_LABEL("Builtins_RecordWrite"));
> __asm__( /* binary instruction stream */ );
> /* Repeat for other builtins. */
>
> extern "C" const uint8_t v8_embedded_blob_[];
> static const uint32_t v8_embedded_blob_size_ = /* size in bytes */;
>
> }  // namespace
>
> const uint8_t* DefaultEmbeddedBlob() { return v8_embedded_blob_; }
> uint32_t DefaultEmbeddedBlobSize() { return v8_embedded_blob_size_; }
>
> }  // namespace internal
> }  // namespace v8
>
> Bug: v8:6666
> Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng;luci.v8.try:v8_linux64_fyi_rel_ng
> Change-Id: Ic989f01da69ebe2863f31d934bfbe2c5d6e80864
> Reviewed-on: https://chromium-review.googlesource.com/946011
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Reviewed-by: Yang Guo <yangguo@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#51759}

TBR=yangguo@chromium.org

Bug: v8:6666
Change-Id: Iba245976ce46c62474dcba94a99ab4a217b2e20e
Cq-Include-Trybots: luci.chromium.try:linux_chromium_rel_ng;luci.v8.try:v8_linux64_fyi_rel_ng
Reviewed-on: https://chromium-review.googlesource.com/950983Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51769}