Added \!con(a,b) syntax to concatnate two dag fragments.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@37063 91177308-0d34-0410-b5e6-96231b3b80d8

utils/TableGen/FileLexer.l.cvs

@@ -206,6 +206,7 @@ field          { return FIELD; }
 let            { return LET; }
 in             { return IN; }
 
+!con           { return CONCATTOK; }
 !sra           { return SRATOK; }
 !srl           { return SRLTOK; }
 !shl           { return SHLTOK; }