Update doxygen comments about lifetime requirements of CXUnsaveFile data arguments.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@101054 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/clang-c/Index.h b/include/clang-c/Index.h
index f7b8475..bfb6481 100644
--- a/include/clang-c/Index.h
+++ b/include/clang-c/Index.h
@@ -609,7 +609,9 @@
  *
  * \param unsaved_files the files that have not yet been saved to disk
  * but may be required for code completion, including the contents of
- * those files.
+ * those files.  The contents and name of these files (as specified by
+ * CXUnsavedFile) are copied when necessary, so the client only needs to
+ * guarantee their validity until the call to this function returns.
  *
  * \param diag_callback callback function that will receive any diagnostics
  * emitted while processing this source file. If NULL, diagnostics will be
@@ -1701,7 +1703,9 @@
  *
  * \param unsaved_files the files that have not yet been saved to disk
  * but may be required for code completion, including the contents of
- * those files.
+ * those files.  The contents and name of these files (as specified by
+ * CXUnsavedFile) are copied when necessary, so the client only needs to
+ * guarantee their validity until the call to this function returns.
  *
  * \param complete_filename the name of the source file where code completion
  * should be performed. In many cases, this name will be the same as the