Add a wrapper for open.

This centralizes the handling of O_BINARY and opens the way for hiding more
differences (like how open behaves with directories).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186447 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/FileSystem.h

@@ -611,6 +611,37 @@ error_code createTemporaryFile(const Twine &Prefix, StringRef Suffix,
 error_code createUniqueDirectory(const Twine &Prefix,
                                  SmallVectorImpl<char> &ResultPath);
 
+enum OpenFlags {
+  F_None = 0,
+
+  /// F_Excl - When opening a file, this flag makes raw_fd_ostream
+  /// report an error if the file already exists.
+  F_Excl = 1,
+
+  /// F_Append - When opening a file, if it already exists append to the
+  /// existing file instead of returning an error.  This may not be specified
+  /// with F_Excl.
+  F_Append = 2,
+
+  /// F_Binary - The file should be opened in binary mode on platforms that
+  /// make this distinction.
+  F_Binary = 4
+};
+
+inline OpenFlags operator|(OpenFlags A, OpenFlags B) {
+  return OpenFlags(unsigned(A) | unsigned(B));
+}
+
+inline OpenFlags &operator|=(OpenFlags &A, OpenFlags B) {
+  A = A | B;
+  return A;
+}
+
+error_code openFileForWrite(const Twine &Name, int &ResultFD, OpenFlags Flags,
+                            unsigned Mode = 0666);
+
+error_code openFileForRead(const Twine &Name, int &ResultFD);
+
 /// @brief Canonicalize path.
 ///
 /// Sets result to the file system's idea of what path is. The result is always