On Darwin switch from the `VM_MEMORY_ANALYSIS_TOOL` VM tag to

`VM_MEMORY_SANITIZER`.

It turns out that `VM_MEMORY_ANALYSIS_TOOL` is already reserved for
use by other tools so switch to a tag reserved for use by the Sanitizers.

rdar://problem/41969783

Differential Revision: https://reviews.llvm.org/D49603

llvm-svn: 337579