Use llvm::sys::fs::createTemporaryFile.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@185717 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Frontend/ASTUnit.cpp b/lib/Frontend/ASTUnit.cpp
index d175073..7d25ebb 100644
--- a/lib/Frontend/ASTUnit.cpp
+++ b/lib/Frontend/ASTUnit.cpp
@@ -1244,7 +1244,7 @@
     return TmpFile;
 
   SmallString<128> Path;
-  llvm::sys::fs::unique_file("preamble-%%%%%%.pch", Path);
+  llvm::sys::fs::createTemporaryFile("preamble", "pch", Path);
 
   return Path.str();
 }