Revert "[turbofan] Remove out-of-line defn of constexpr vars"

This reverts commit 05da6708.

Reason for revert: Guess I was wrong: https://ci.chromium.org/ui/p/v8/builders/ci/V8%20Clusterfuzz%20Linux64%20ASAN%20no%20inline%20-%20release%20builder/25729/overview

Original change's description:
> [turbofan] Remove out-of-line defn of constexpr vars
>
> It's deprecated in C++17 and not needed (it was needed for
> static const, but not for constexpr)
>
> Bug: chromium:1274247
> Change-Id: If92d7b6300493cb186ff2ade8f6b6a4820d5a264
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3306429
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Jakob Gruber <jgruber@chromium.org>
> Auto-Submit: Leszek Swirski <leszeks@chromium.org>
> Reviewed-by: Jakob Gruber <jgruber@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78149}

Bug: chromium:1274247
Change-Id: I26f8377b331895363fec5329a08261ebec3696ef
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3306431
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Owners-Override: Leszek Swirski <leszeks@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@{#78152}

src/compiler/js-heap-broker.cc

@@ -30,6 +30,11 @@ namespace compiler {
 
 #define TRACE(broker, x) TRACE_BROKER(broker, x)
 
+// These definitions are here in order to please the linker, which in debug mode
+// sometimes requires static constants to be defined in .cc files.
+const uint32_t JSHeapBroker::kMinimalRefsBucketCount;
+const uint32_t JSHeapBroker::kInitialRefsBucketCount;
+
 void JSHeapBroker::IncrementTracingIndentation() { ++trace_indentation_; }
 
 void JSHeapBroker::DecrementTracingIndentation() { --trace_indentation_; }