Disable CFI icall for v8::internal::MemMove.

MemMove makes an indirect call to memmove_function which is
overwritten in init_memcopy_functions to an address not
permitted by CFI to be called indirectly.

This CL disables CFI_ICALL for this function.

BUG=chromium:584575

Change-Id: I372f0c13a1900bf3c48484db9ba7ff4a3b3fc7e9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2289010Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Will Harris <wfh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68766}

src/utils/memcopy.cc

@@ -18,6 +18,7 @@ static void MemMoveWrapper(void* dest, const void* src, size_t size) {
 static MemMoveFunction memmove_function = &MemMoveWrapper;
 
 // Copy memory area to disjoint memory area.
+DISABLE_CFI_ICALL
 V8_EXPORT_PRIVATE void MemMove(void* dest, const void* src, size_t size) {
   if (size == 0) return;
   // Note: here we rely on dependent reads being ordered. This is true