COMP: Fix rule hash code during bootstrap

During bootstrap we do not bother with rule hashing.  This updates the
dummy implementation to account for the recent change in rule hash
method signatures.

Source/cmGlobalGenerator.cxx

@@ -2035,8 +2035,7 @@ cmGlobalGenerator::AddRuleHash(const std::vector<std::string>& outputs,
   this->RuleHashes[fname] = hash;
 #else
   (void)outputs;
-  (void)first;
-  (void)last;
+  (void)content;
 #endif
 }