[sparkplug] Make --short-builtin-calls flag modifiable

The feature is controlled by a boolean flag on Isolate, so there's no
need to keep the flag read-only.

Bug: v8:11527, chromium:1241665
Change-Id: I377452fed10b319a4a512c090706c754603c2ae8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3270547
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#77820}

src/flags/flag-definitions.h

@@ -1741,12 +1741,9 @@ DEFINE_BOOL(experimental_flush_embedded_blob_icache, true,
             "Used in an experiment to evaluate icache flushing on certain CPUs")
 
 // Flags for short builtin calls feature
-#undef FLAG
 #if V8_SHORT_BUILTIN_CALLS
-#define FLAG FLAG_FULL
 #define V8_SHORT_BUILTIN_CALLS_BOOL true
 #else
-#define FLAG FLAG_READONLY
 #define V8_SHORT_BUILTIN_CALLS_BOOL false
 #endif
 
@@ -1754,9 +1751,6 @@ DEFINE_BOOL(short_builtin_calls, V8_SHORT_BUILTIN_CALLS_BOOL,
             "Put embedded builtins code into the code range for shorter "
             "builtin calls/jumps if system has >=4GB memory")
 
-#undef FLAG
-#define FLAG FLAG_FULL
-
 // runtime.cc
 DEFINE_BOOL(runtime_call_stats, false, "report runtime call counts and times")
 DEFINE_GENERIC_IMPLICATION(