Add an addition operator to TableGen

This adds an !add(a, b) operator to tablegen; this will be used
to cleanup the PPC register definitions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173445 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/TableGen/TGLexer.cpp b/lib/TableGen/TGLexer.cpp
index d733f14..e75abcf 100644
--- a/lib/TableGen/TGLexer.cpp
+++ b/lib/TableGen/TGLexer.cpp
@@ -462,6 +462,7 @@
     .Case("head", tgtok::XHead)
     .Case("tail", tgtok::XTail)
     .Case("con", tgtok::XConcat)
+    .Case("add", tgtok::XADD)
     .Case("shl", tgtok::XSHL)
     .Case("sra", tgtok::XSRA)
     .Case("srl", tgtok::XSRL)