Update LLVM (#742)

* Replace enum compatibility synonyms that have now been removed
diff --git a/lib/Compiler.cpp b/lib/Compiler.cpp
index b932dc8..e4cd7a7 100644
--- a/lib/Compiler.cpp
+++ b/lib/Compiler.cpp
@@ -893,7 +893,7 @@
                    std::string output) {
   std::error_code ec;
   std::unique_ptr<llvm::ToolOutputFile> out(
-      new llvm::ToolOutputFile(output, ec, llvm::sys::fs::F_None));
+      new llvm::ToolOutputFile(output, ec, llvm::sys::fs::OF_None));
   if (ec) {
     llvm::errs() << output << ": " << ec.message() << '\n';
     return -1;