[baseline] Temporarily disable concurrent sparkplug

... in order to prepare for smoother rollout via the finch flag.

Bug: v8:12054, chromium:1343515
Change-Id: I24f51b73daa35c8de6967e8eb088dd3bee95fc4f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3755120Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81659}

src/flags/flag-definitions.h

@@ -725,7 +725,7 @@ 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, true,
+DEFINE_BOOL(concurrent_sparkplug, false,
             "compile Sparkplug code in a background thread")
 DEFINE_WEAK_IMPLICATION(future, concurrent_sparkplug)
 DEFINE_NEG_IMPLICATION(predictable, concurrent_sparkplug)
@@ -733,7 +733,7 @@ DEFINE_NEG_IMPLICATION(single_threaded, concurrent_sparkplug)
 DEFINE_NEG_IMPLICATION(jitless, concurrent_sparkplug)
 #endif
 DEFINE_UINT(
-    concurrent_sparkplug_max_threads, 2,
+    concurrent_sparkplug_max_threads, 0,
     "max number of threads that concurrent Sparkplug can use (0 for unbounded)")
 DEFINE_BOOL(concurrent_sparkplug_high_priority_threads, false,
             "use high priority compiler threads for concurrent Sparkplug")