Update v8 to run on iPhone

iOS uses 16kb memory pages. This change modifies OS::GetRandomMmapAddr()
to return a 16kb-aligned address on apple ARM64.

The mrs instruction is invalid on iOS. This change modifies
CacheLineSizes::CacheLineSizes() so that mrs is not executed.

Change-Id: I13fcc8498e715c03432c7a652ee723660f746069
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1701127Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62730}

AUTHORS

@@ -172,6 +172,7 @@ Sandro Santilli <strk@keybit.net>
 Sanjoy Das <sanjoy@playingwithpointers.com>
 Seo Sanghyeon <sanxiyn@gmail.com>
 Shawn Anastasio <shawnanastasio@gmail.com>
+Shawn Presser <shawnpresser@gmail.com>
 Stefan Penner <stefan.penner@gmail.com>
 Sylvestre Ledru <sledru@mozilla.com>
 Taketoshi Aono <brn@b6n.ch>

src/base/platform/platform-posix.cc

@@ -199,6 +199,12 @@ void* OS::GetRandomMmapAddr() {
     MutexGuard guard(rng_mutex.Pointer());
     GetPlatformRandomNumberGenerator()->NextBytes(&raw_addr, sizeof(raw_addr));
   }
+#if defined(__APPLE__)
+#if V8_TARGET_ARCH_ARM64
+  DCHECK_EQ(1 << 14, AllocatePageSize());
+  raw_addr = RoundDown(raw_addr, 1 << 14);
+#endif
+#endif
 #if defined(V8_USE_ADDRESS_SANITIZER) || defined(MEMORY_SANITIZER) || \
     defined(THREAD_SANITIZER) || defined(LEAK_SANITIZER)
   // If random hint addresses interfere with address ranges hard coded in

src/codegen/arm64/cpu-arm64.cc

@@ -15,7 +15,7 @@ namespace internal {
 class CacheLineSizes {
  public:
   CacheLineSizes() {
-#if !defined(V8_HOST_ARCH_ARM64) || defined(V8_OS_WIN)
+#if !defined(V8_HOST_ARCH_ARM64) || defined(V8_OS_WIN) || defined(__APPLE__)
     cache_type_register_ = 0;
 #else
     // Copy the content of the cache type register to a core register.