ARM: Use ubfx and movw instructions to avoid a PC-relative load on

src/platform.h

Index: src/platform.h
===================================================================
--- src/platform.h	(revision 10578)
+++ src/platform.h	(working copy)
@@ -323,7 +323,8 @@
   // Reserves virtual memory containing an area of the given size that
   // is aligned per alignment. This may not be at the position returned
   // by address().
-  VirtualMemory(size_t size, size_t alignment);
+  VirtualMemory(
+      size_t size, size_t alignment, intptr_t preferred_placement = 0);
 
   // Releases the reserved memory, if any, controlled by this VirtualMemory
   // object.