Revert "r372201: [Support] Replace function with function_ref in writeFileAtomically. NFC"

function_ref causes calls to the function to be ambiguous, breaking
compilation.

Reverting for now.

llvm-svn: 372202

Author: ilya-biryukov

llvm/include/llvm/Support/FileUtilities.h

@@ -14,7 +14,6 @@
 #ifndef LLVM_SUPPORT_FILEUTILITIES_H
 #define LLVM_SUPPORT_FILEUTILITIES_H
 
-#include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -108,9 +107,9 @@ namespace llvm {
   llvm::Error writeFileAtomically(StringRef TempPathModel, StringRef FinalPath,
                                   StringRef Buffer);
 
-  llvm::Error writeFileAtomically(
-      StringRef TempPathModel, StringRef FinalPath,
-      llvm::function_ref<llvm::Error(llvm::raw_ostream &)> Writer);
+  llvm::Error
+  writeFileAtomically(StringRef TempPathModel, StringRef FinalPath,
+                      std::function<llvm::Error(llvm::raw_ostream &)> Writer);
 } // End llvm namespace
 
 #endif

llvm/lib/Support/FileUtilities.cpp

@@ -296,7 +296,7 @@ llvm::Error llvm::writeFileAtomically(StringRef TempPathModel,
 
 llvm::Error llvm::writeFileAtomically(
     StringRef TempPathModel, StringRef FinalPath,
-    llvm::function_ref<llvm::Error(llvm::raw_ostream &)> Writer) {
+    std::function<llvm::Error(llvm::raw_ostream &)> Writer) {
   SmallString<128> GeneratedUniqPath;
   int TempFD;
   if (sys::fs::createUniqueFile(TempPathModel.str(), TempFD,