Reland "Reland "[baseline] Enable concurrent sparkplug""

This reverts commit 5d6a16fb.

Reason for revert: it was a flake

Original change's description:
> Revert "Reland "[baseline] Enable concurrent sparkplug""
>
> This reverts commit fee91f9a.
>
> Reason for revert: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Mac64/44699/overview
>
> Original change's description:
> > Reland "[baseline] Enable concurrent sparkplug"
> >
> > Issue that cause the revert was fixed: v8:12713
> > https://bugs.chromium.org/p/v8/issues/detail?id=12713
> >
> > This is a reland of commit f01a6098
> >
> > Original change's description:
> > > [baseline] Enable concurrent sparkplug
> > >
> > > Bug: v8:12054
> > > Change-Id: I1b0ee1a9541a75412b882b259e421aa6e88317da
> > > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3259658
> > > Auto-Submit: Victor Gomes <victorgomes@chromium.org>
> > > Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> > > Commit-Queue: Toon Verwaest <verwaest@chromium.org>
> > > Cr-Commit-Position: refs/heads/main@{#79485}
> >
> > Bug: v8:12054
> > Change-Id: Iafba22e3fa3b38eddb226db6cd5afdb7e3e6b435
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3528992
> > Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> > Commit-Queue: Victor Gomes <victorgomes@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#79618}
>
> Bug: v8:12054
> Change-Id: I3ba60433fdbb5617900c83d022e4dd6f830695f9
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3550271
> Auto-Submit: Tobias Tebbi <tebbi@chromium.org>
> Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> Owners-Override: Tobias Tebbi <tebbi@chromium.org>
> Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Cr-Commit-Position: refs/heads/main@{#79619}

Bug: v8:12054
Change-Id: Ia0fe1df00f5e715ceda46fbcdc48aed0f0190362
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3550272
Owners-Override: Tobias Tebbi <tebbi@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#79622}

src/flags/flag-definitions.h

@@ -713,7 +713,7 @@ DEFINE_BOOL(baseline_batch_compilation, true, "batch compile Sparkplug code")
 DEFINE_BOOL_READONLY(concurrent_sparkplug, false,
                      "compile Sparkplug code in a background thread")
 #else
-DEFINE_BOOL(concurrent_sparkplug, false,
+DEFINE_BOOL(concurrent_sparkplug, true,
             "compile Sparkplug code in a background thread")
 DEFINE_WEAK_IMPLICATION(future, concurrent_sparkplug)
 DEFINE_NEG_IMPLICATION(predictable, concurrent_sparkplug)
@@ -721,7 +721,7 @@ DEFINE_NEG_IMPLICATION(single_threaded, concurrent_sparkplug)
 DEFINE_NEG_IMPLICATION(jitless, concurrent_sparkplug)
 #endif
 DEFINE_UINT(
-    concurrent_sparkplug_max_threads, 0,
+    concurrent_sparkplug_max_threads, 2,
     "max number of threads that concurrent Sparkplug can use (0 for unbounded)")
 #else
 DEFINE_BOOL(baseline_batch_compilation, false, "batch compile Sparkplug code")