disable use of arm memcpy asm if building as thumb code

the thumb incompatibilities in the asm are probably only minor and
should be fixable, but for now just use the C version.

src/string/arm/memcpy.c

-#if __ARMEB__
+#if __ARMEB__ || __thumb__
 #include "../memcpy.c"
 #endif

src/string/arm/memcpy_le.S

-#ifndef __ARMEB__
+#if !__ARMEB__ && !__thumb__
 
 /*
  * Copyright (C) 2008 The Android Open Source Project