Removing LLVM's allocator from CFI

The Linux CFI bot was detecting unrelated casts in LLVM's allocator,
which is actually the desired behavior of an allocator, generally. Added
an entry to the blacklist to prevent this error on the CFI bot.

R=vtsyrklevich@chromium.org
TBR=pcc@chromium.org

Bug: 726075
Change-Id: I7fd970a5f564d46a066ae57a0d7c6fe46be62868
Reviewed-on: https://chromium-review.googlesource.com/688017Reviewed-by: Alexis Hétu <sugoi@chromium.org>
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504754}

tools/cfi/blacklist.txt

@@ -13,6 +13,9 @@ fun:*ThreadSpecific*
 # Mesa contains several bad casts.
 src:*third_party/mesa*
 
+# LLVM's allocator
+src:*third_party/swiftshader/third_party/llvm-subzero/include/llvm/Support/Allocator.h*
+
 # Deliberate bad cast to derived class to hide functions.
 type:*BlockIUnknownMethods*
 type:*BlockRefType*