Update LLVM for rebase to r212749.

Includes a cherry-pick of:
r212948 - fixes a small issue with atomic calls

Change-Id: Ib97bd980b59f18142a69506400911a6009d9df18
diff --git a/lib/Support/StringPool.cpp b/lib/Support/StringPool.cpp
index ff607cf..76faabc 100644
--- a/lib/Support/StringPool.cpp
+++ b/lib/Support/StringPool.cpp
@@ -27,7 +27,7 @@
   if (I != InternTable.end())
     return PooledStringPtr(&*I);
   
-  entry_t *S = entry_t::Create(Key.begin(), Key.end());
+  entry_t *S = entry_t::Create(Key);
   S->getValue().Pool = this;
   InternTable.insert(S);