Turn cl::values() (for enum) from a vararg function to using C++ variadic template

The core of the change is supposed to be NFC, however it also fixes
what I believe was an undefined behavior when calling:

 va_start(ValueArgs, Desc);

with Desc being a StringRef.

Differential Revision: https://reviews.llvm.org/D25342

llvm-svn: 283671
diff --git a/llvm/utils/TableGen/TableGen.cpp b/llvm/utils/TableGen/TableGen.cpp
index 24dbe5d..1847b58 100644
--- a/llvm/utils/TableGen/TableGen.cpp
+++ b/llvm/utils/TableGen/TableGen.cpp
@@ -91,8 +91,7 @@
                     clEnumValN(GenAttributes, "gen-attrs",
                                "Generate attributes"),
                     clEnumValN(GenSearchableTables, "gen-searchable-tables",
-                               "Generate generic binary-searchable table"),
-                    clEnumValEnd));
+                               "Generate generic binary-searchable table")));
 
   cl::opt<std::string>
   Class("class", cl::desc("Print Enum list for this class"),