[platform] Add Permission::kNoAccessWillJitLater enum value

This value is unused for now. This CL is part 1 of a 3-step dance.
Part 2 will be teaching Chrome's Platform implementation to accept
the new value. Part 3 will then actually use it in V8.

Bug: chromium:1117591
Change-Id: Ie3aed20d4cc58f3def3be2a3a03bba4c3a37bf44
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2450056
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70335}

include/v8-platform.h

@@ -383,7 +383,13 @@ class PageAllocator {
     kReadWrite,
     // TODO(hpayer): Remove this flag. Memory should never be rwx.
     kReadWriteExecute,
-    kReadExecute
+    kReadExecute,
+    // Set this when reserving memory that will later require kReadWriteExecute
+    // permissions. The resulting behavior is platform-specific, currently
+    // this is used to set the MAP_JIT flag on Apple Silicon.
+    // TODO(jkummerow): Remove this when Wasm has a platform-independent
+    // w^x implementation.
+    kNoAccessWillJitLater
   };
 
   /**

test/unittests/heap/unmapper-unittest.cc

@@ -170,6 +170,7 @@ class TrackingPageAllocator : public ::v8::PageAllocator {
     os << "  page: [" << start << ", " << end << "), access: ";
     switch (access) {
       case PageAllocator::kNoAccess:
+      case PageAllocator::kNoAccessWillJitLater:
         os << "--";
         break;
       case PageAllocator::kRead: