[mac][wasm] Work around MacOS 11.2 code page decommit failures

MacOS 11.2 refuses to set "no access" permissions on memory that
we previously used for JIT-compiled code. It is still unclear
whether this is WAI on the part of the kernel. In the meantime,
as a workaround, we use madvise(..., MADV_FREE_REUSABLE) instead
of mprotect(..., NONE) when discarding code pages. This is inspired
by what Chromium's gin platform does.

Fixed: v8:11389
Change-Id: I866586932573b4253002436ae5eee4e0411c45fc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2679688
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72559}

src/base/platform/platform-posix.cc

@@ -415,6 +415,16 @@ bool OS::SetPermissions(void* address, size_t size, MemoryPermission access) {
 
   int prot = GetProtectionFromMemoryPermission(access);
   int ret = mprotect(address, size, prot);
+
+  // MacOS 11.2 on Apple Silicon refuses to switch permissions from
+  // rwx to none. Just use madvise instead.
+#if defined(V8_OS_MACOSX)
+  if (ret != 0 && access == OS::MemoryPermission::kNoAccess) {
+    ret = madvise(address, size, MADV_FREE_REUSABLE);
+    return ret == 0;
+  }
+#endif
+
   if (ret == 0 && access == OS::MemoryPermission::kNoAccess) {
     // This is advisory; ignore errors and continue execution.
     USE(DiscardSystemPages(address, size));