[GSoC] Flag value completion for clang

This is patch for GSoC project, bash-completion for clang.

To use this on bash, please run `source clang/utils/bash-autocomplete.sh`.
bash-autocomplete.sh is code for bash-completion.

In this patch, Options.td was mainly changed in order to add value class
in Options.inc.

llvm-svn: 305805
diff --git a/llvm/lib/Option/Option.cpp b/llvm/lib/Option/Option.cpp
index 4832e65..bf9f040 100644
--- a/llvm/lib/Option/Option.cpp
+++ b/llvm/lib/Option/Option.cpp
@@ -47,6 +47,7 @@
     P(UnknownClass);
     P(FlagClass);
     P(JoinedClass);
+    P(ValuesClass);
     P(SeparateClass);
     P(CommaJoinedClass);
     P(MultiArgClass);