Revert "Rename F_{None,Text,Append} to OF_{None,Text,Append}. NFC"

This reverts commit 58c814614d2ac69bcf79b09543505fac80ada4e6.
Fixes build breakage using LLVM<7.

git-svn-id: https://llvm.org/svn/llvm-project/libclc/trunk@367893 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/utils/prepare-builtins.cpp b/utils/prepare-builtins.cpp
index 550b597..de1e804 100644
--- a/utils/prepare-builtins.cpp
+++ b/utils/prepare-builtins.cpp
@@ -95,10 +95,10 @@
   std::error_code EC;
 #if HAVE_LLVM >= 0x0600
   std::unique_ptr<ToolOutputFile> Out(
-      new ToolOutputFile(OutputFilename, EC, sys::fs::OF_None));
+      new ToolOutputFile(OutputFilename, EC, sys::fs::F_None));
 #else
   std::unique_ptr<tool_output_file> Out(
-      new tool_output_file(OutputFilename, EC, sys::fs::OF_None));
+      new tool_output_file(OutputFilename, EC, sys::fs::F_None));
 #endif
   if (EC) {
     errs() << EC.message() << '\n';