[NFC][DFSan] Cleanup code to use align functions.

[morehouse]

LGTM

compiler-rt/lib/dfsan/dfsan.cpp

if (!MEM_IS_SHADOW(shadow_for(dst)) ||
       !MEM_IS_SHADOW(shadow_for((void *)((uptr)src + size)))) {
     CHECK(false);
     return;
   }
   // If destination origin range overlaps with source origin range, move
   // origins by copying origins in a reverse order; otherwise, copy origins in
   // a normal order. The orders of origin transfer are consistent with the
   // orders of how memcpy and memmove transfer user data.
-  uptr src_aligned_beg = reinterpret_cast<uptr>(src) & ~3UL;
-  uptr src_aligned_end = (reinterpret_cast<uptr>(src) + size) & ~3UL;
-  uptr dst_aligned_beg = reinterpret_cast<uptr>(dst) & ~3UL;
+  uptr src_aligned_beg = OriginAlignDown((uptr)src);
+  uptr src_aligned_end = OriginAlignDown((uptr)src + size);
+  uptr dst_aligned_beg = OriginAlignDown((uptr)dst);
   if (dst_aligned_beg < src_aligned_end && dst_aligned_beg >= src_aligned_beg)
     return ReverseCopyOrigin(dst, src, size, stack);
   return CopyOrigin(dst, src, size, stack);
 }
 
 // Set the size bytes from the addres dst to be the origin value.
 static void SetOrigin(const void *dst, uptr size, u32 origin) {
   if (size == 0)