Use NtCurrentTeb() in GetStackStart() to fix 64-bit Wine on macOS

When running 64-bit Windows binaries on macOS using Wine, there is a
conflict between macOS's use of GS to point to pthread thread-specific
data, and Windows' use of GS to point to the TEB.

Apple has reserved some TSD slots for use by Wine to store commonly-used
TEB members (such as 0x30, the 'Self' pointer to the TEB).
But, other direct GS accesses by Windows programs (such as to
'StackBase') will return macOS pthread data rather than the TEB member.
This was causing a V8 unit test to crash on macOS under Wine.

Using NtCurrentTeb() gets the 'Self' pointer first, then dereferences
it to access the correct 'StackBase', fixing the crash.
This turns GetStackStart() from one instruction into two.

Chrome (http://crrev.com/c/2380425) and Crashpad also use
NtCurrentTeb().

The 32-bit change isn't needed, but is just for consistency.

Bug: chromium:1121842
Change-Id: I824f893aa451d8570142226be91840c964426f38
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2381941Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69627}

AUTHORS

@@ -40,6 +40,7 @@ Groupon <*@groupon.com>
 Meteor Development Group <*@meteor.com>
 Cloudflare, Inc. <*@cloudflare.com>
 Julia Computing, Inc. <*@juliacomputing.com>
+CodeWeavers, Inc. <*@codeweavers.com>
 
 Aaron Bieber <deftly@gmail.com>
 Aaron O'Mullan <aaron.omullan@gmail.com>

src/base/platform/platform-win32.cc

@@ -1397,9 +1397,11 @@ void OS::AdjustSchedulingParams() {}
 // static
 void* Stack::GetStackStart() {
 #if defined(V8_TARGET_ARCH_X64)
-  return reinterpret_cast<void*>(__readgsqword(offsetof(NT_TIB64, StackBase)));
+  return reinterpret_cast<void*>(
+      reinterpret_cast<NT_TIB64*>(NtCurrentTeb())->StackBase);
 #elif defined(V8_TARGET_ARCH_32_BIT)
-  return reinterpret_cast<void*>(__readfsdword(offsetof(NT_TIB, StackBase)));
+  return reinterpret_cast<void*>(
+      reinterpret_cast<NT_TIB*>(NtCurrentTeb())->StackBase);
 #elif defined(V8_TARGET_ARCH_ARM64)
   // Windows 8 and later, see
   // https://docs.microsoft.com/en-us/windows/win32/api/processthreadsapi/nf-processthreadsapi-getcurrentthreadstacklimits