[HWASan] Update HWASan assembly snippet in the docs

[alekseyshl]

Summary

To complement https://reviews.llvm.org/D45840

[kcc]

LGTM

cfe/trunk/docs/HardwareAssistedAddressSanitizerDesign.rst

 verifies the tags. Currently, the following sequence is used:
 
 
 .. code-block:: asm
 
   // int foo(int *a) { return *a; }
   // clang -O2 --target=aarch64-linux -fsanitize=hwaddress -c load.c
   foo:
-       0:  08 dc 44 d3   ubfx  x8, x0, #4, #52  // shadow address
-       4:  08 01 40 39   ldrb  w8, [x8]         // load shadow
-       8:  09 fc 78 d3   lsr  x9, x0, #56      // address tag
-       c:  3f 01 08 6b   cmp  w9, w8           // compare tags
-      10:  61 00 00 54   b.ne  #12              // jump on mismatch
-      14:  00 00 40 b9   ldr  w0, [x0]         // original load
-      18:  c0 03 5f d6   ret
-      1c:  40 20 21 d4   brk  #0x902           // trap
-
+       0:  08 00 00 90   adrp  x8, 0 <__hwasan_shadow>
+       4:  08 01 40 f9   ldr  x8, [x8]         // shadow base (to be resolved by the loader)
+       8:  09 dc 44 d3   ubfx  x9, x0, #4, #52  // shadow offset
+       c:  28 69 68 38   ldrb  w8, [x9, x8]     // load shadow tag
+      10:  09 fc 78 d3   lsr  x9, x0, #56      // extract address tag
+      14:  3f 01 08 6b   cmp  w9, w8           // compare tags
+      18:  61 00 00 54   b.ne  24               // jump on mismatch
+      1c:  00 00 40 b9   ldr  w0, [x0]         // original load
+      20:  c0 03 5f d6   ret
+      24:  40 20 21 d4   brk  #0x902           // trap
 
 Alternatively, memory accesses are prefixed with a function call.
 
 Heap
 ----
 
 Tagging the heap memory/pointers is done by `malloc`.
 This can be based on any malloc that forces all objects to be TG-aligned.