Merge recent changes from LLVM's lib/Support/Atomic.cpp

In particular, https://reviews.llvm.org/D36281

Bug: chromium:495204
Change-Id: I48afb5b8dd594ce1b43c6ca9fb20638d40119236
Reviewed-on: https://swiftshader-review.googlesource.com/11248
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nico Weber <thakis@google.com>
diff --git a/third_party/llvm-subzero/lib/Support/Atomic.cpp b/third_party/llvm-subzero/lib/Support/Atomic.cpp
index 80550e2..7328a93 100644
--- a/third_party/llvm-subzero/lib/Support/Atomic.cpp
+++ b/third_party/llvm-subzero/lib/Support/Atomic.cpp
@@ -17,7 +17,9 @@
 using namespace llvm;
 
 #if defined(_MSC_VER)
-#include <Intrin.h>
+#include <intrin.h>
+
+// We must include windows.h after intrin.h.
 #include <windows.h>
 #undef MemoryFence
 #endif