Fix building Reactor with the latest LLVM revision

llvm/Pass.h is no longer included by the other headers we depend on, so
include it explicitly.

This upstreams the change from cl/425862763.

Bug: b/165000222
Change-Id: I06e1c4596c028373ac40ee8969a4a0842f2c3aa6
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/62148
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Sean Risser <srisser@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>

src/Reactor/LLVMReactor.cpp

diff --git a/src/Reactor/LLVMReactor.cpp b/src/Reactor/LLVMReactor.cpp
index 30edadf..86799a6 100644
--- a/src/Reactor/LLVMReactor.cpp
+++ b/src/Reactor/LLVMReactor.cpp
@@ -26,6 +26,7 @@
 #include "llvm/IR/IntrinsicsX86.h"
 #include "llvm/IR/LegacyPassManager.h"
 #include "llvm/IR/Verifier.h"
+#include "llvm/Pass.h"
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Transforms/Coroutines.h"