Add v8_os_page_size flag for cross compilation

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index ef9a455e868de87d3362fe54a3ec9d18360b97a8..f5701adc69edc2a80cee6125e1eb780516e0fddb 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -1090,7 +1090,7 @@ class SkipList {
 
 // ----------------------------------------------------------------------------
 // A space acquires chunks of memory from the operating system. The memory
-// allocator allocated and deallocates pages for the paged heap spaces and large
+// allocator allocates and deallocates pages for the paged heap spaces and large
 // pages for large object space.
 class MemoryAllocator {
  public:
@@ -1209,6 +1209,8 @@ class MemoryAllocator {
                                  : Page::kAllocatableMemory;
   }
 
+  static intptr_t GetCommitPageSize();
+
   explicit MemoryAllocator(Isolate* isolate);
 
   // Initializes its internal bookkeeping structures.