base: Clean up redundant string functions and use C++11

This patch does a bit of housekeeping on the string helper functions
and relies on the C++11 standard library where possible. It also does
away with our custom string hash as an implementation is already part
of the standard library.

src/cpu/o3/lsq_unit_impl.hh

@@ -215,7 +215,7 @@ LSQUnit<Impl>::name() const
     if (Impl::MaxThreads == 1) {
         return iewStage->name() + ".lsq";
     } else {
-        return iewStage->name() + ".lsq.thread" + to_string(lsqID);
+        return iewStage->name() + ".lsq.thread" + std::to_string(lsqID);
     }
 }