Avoid TRUE and FALSE which apparently conflict with some macros on OSX

llvm-svn: 12566
diff --git a/llvm/lib/AsmParser/Lexer.l b/llvm/lib/AsmParser/Lexer.l
index 3203fe5..510fedb 100644
--- a/llvm/lib/AsmParser/Lexer.l
+++ b/llvm/lib/AsmParser/Lexer.l
@@ -174,8 +174,8 @@
 
 begin           { return BEGINTOK; }
 end             { return ENDTOK; }
-true            { return TRUE;  }
-false           { return FALSE; }
+true            { return TRUETOK;  }
+false           { return FALSETOK; }
 declare         { return DECLARE; }
 global          { return GLOBAL; }
 constant        { return CONSTANT; }