[gwp_asan] Use zx_system_get_page_size() on Fuchsia

[mcgrathr]

Summary

Fuchsia is migrating to a variable page size.

[mcgrathr]

remove obsolete #include

compiler-rt/lib/gwp_asan/platform_specific/guarded_pool_allocator_fuchsia.cpp

 //===-- guarded_pool_allocator_fuchsia.cpp ----------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "gwp_asan/guarded_pool_allocator.h"
 #include "gwp_asan/utilities.h"
 
 #include <assert.h>
 #include <stdint.h>
 #include <string.h>
 #include <zircon/limits.h>
 #include <zircon/process.h>
 #include <zircon/syscalls.h>
 
 namespace gwp_asan {
 void GuardedPoolAllocator::initPRNG() {
   _zx_cprng_draw(&getThreadLocals()->RandomState, sizeof(uint32_t));
 }
 
void GuardedPoolAllocator::deallocateInGuardedPool(void *Ptr,
   assert((Size % State.PageSize) == 0);
   const zx_handle_t Vmar = GuardedPagePoolPlatformData.Vmar;
   assert(Vmar != ZX_HANDLE_INVALID && Vmar != _zx_vmar_root_self());
   const zx_status_t Status =
       _zx_vmar_unmap(Vmar, reinterpret_cast<zx_vaddr_t>(Ptr), Size);
   Check(Status == ZX_OK, "Vmar unmapping failed");
 }
 
-size_t GuardedPoolAllocator::getPlatformPageSize() { return ZX_PAGE_SIZE; }
+size_t GuardedPoolAllocator::getPlatformPageSize() {
+  return _zx_system_get_page_size();
+}
 
 void GuardedPoolAllocator::installAtFork() {}
 } // namespace gwp_asan