Implement constant pointers, and null specifically in the parser, bytecode writer, and
bytecode reader.

llvm-svn: 668
diff --git a/llvm/lib/AsmParser/Lexer.l b/llvm/lib/AsmParser/Lexer.l
index 84062e7..06b197d 100644
--- a/llvm/lib/AsmParser/Lexer.l
+++ b/llvm/lib/AsmParser/Lexer.l
@@ -128,6 +128,7 @@
 implementation  { return IMPLEMENTATION; }
 \.\.\.          { return DOTDOTDOT; }
 string          { return STRING; }
+null            { return NULL_TOK; }
 
 void            { llvmAsmlval.PrimType = Type::VoidTy  ; return VOID;   }
 bool            { llvmAsmlval.PrimType = Type::BoolTy  ; return BOOL;   }