ruby: fix slicc compiler to complain about duplicate symbols

Previously, .sm files were allowed to use the same name for a type and a
variable. This is unnecessarily confusing and has some bad side effects, like
not being able to declare later variables in the same scope with the same type.
This causes the compiler to complain and die on things like Address Address.

Committed by: Nilay Vaish <nilay@cs.wisc.edu>

src/mem/slicc/symbols/SymbolTable.py

@@ -68,6 +68,11 @@ class SymbolTable(object):
         if id in self.sym_map_vec[-1]:
             sym.error("Symbol '%s' redeclared in same scope.", id)
 
+        for sym_map in self.sym_map_vec:
+            if id in sym_map:
+                if type(self.sym_map_vec[0][id]) != type(sym):
+                    sym.error("Conflicting declaration of Symbol '%s'", id)
+
         # FIXME - warn on masking of a declaration in a previous frame
         self.sym_map_vec[-1][id] = sym