deps: V8: cherry-pick 215ccd593edb

Original commit message:

    Use FlagValue::value() in SLOW_DCHECK

    Previously SLOW_DCHECK used the non-constexpr bool() operator
    of FlagValue, which cannot be used in constexpr. Switch to
    FlagValue::value() instead for make it compile in constexpr.

    Change-Id: I3e4f70d82c0027cf56999b6c4639479606151696
    Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/4341495
    Reviewed-by: Jakob Linke <jgruber@chromium.org>
    Commit-Queue: Joyee Cheung <joyee@igalia.com>
    Cr-Commit-Position: refs/heads/main@{#86611}

Refs: v8/v8@215ccd5
PR-URL: #47212
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Debadree Chatterjee <debadree333@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>

common.gypi

@@ -36,7 +36,7 @@
 
     # Reset this number to 0 on major V8 upgrades.
     # Increment by one for each non-official patch applied to deps/v8.
-    'v8_embedder_string': '-node.14',
+    'v8_embedder_string': '-node.15',
 
     ##### V8 defaults for Node.js #####
 

deps/v8/src/common/checks.h

@@ -15,7 +15,7 @@
 
 #ifdef ENABLE_SLOW_DCHECKS
 #define SLOW_DCHECK(condition) \
-  CHECK(!v8::internal::FLAG_enable_slow_asserts || (condition))
+  CHECK(!v8::internal::v8_flags.enable_slow_asserts.value() || (condition))
 #define SLOW_DCHECK_IMPLIES(lhs, rhs) SLOW_DCHECK(!(lhs) || (rhs))
 #else
 #define SLOW_DCHECK(condition) ((void)0)