Lower initial dict/set size from 64->8

By switching to our DenseMap/Set fork with that allows parameterizing
on this.

This is the same number that CPython uses.  We were previously
using llvm's default of 64, which is pretty high -- probably fine
for their use cases, but in Python programs with lots of sets/dicts
we spend a lot of time doing malloc() for all those 1kB+ allocations.
This also increases the time it takes to iterate over the dict/set,
since there are more empty buckets that have to be read + skipped.

src/runtime/set.h

@@ -15,8 +15,7 @@
 #ifndef PYSTON_RUNTIME_SET_H
 #define PYSTON_RUNTIME_SET_H
 
-#include "llvm/ADT/DenseSet.h"
-
+#include "core/from_llvm/DenseSet.h"
 #include "core/types.h"
 #include "runtime/types.h"
 
@@ -29,7 +28,7 @@ extern "C" Box* createSet();
 
 class BoxedSet : public Box {
 public:
-    typedef llvm::DenseSet<BoxAndHash, BoxAndHash::Comparisons> Set;
+    typedef pyston::DenseSet<BoxAndHash, BoxAndHash::Comparisons, /* MinSize= */ 8> Set;
     Set s;
     Box** weakreflist; /* List of weak references */
 

src/runtime/types.h

@@ -24,6 +24,7 @@
 
 #include "codegen/irgen/future.h"
 #include "core/contiguous_map.h"
+#include "core/from_llvm/DenseMap.h"
 #include "core/threading.h"
 #include "core/types.h"
 #include "gc/gc_alloc.h"
@@ -707,7 +708,8 @@ struct BoxAndHash {
 
 class BoxedDict : public Box {
 public:
-    typedef llvm::DenseMap<BoxAndHash, Box*, BoxAndHash::Comparisons> DictMap;
+    typedef pyston::DenseMap<BoxAndHash, Box*, BoxAndHash::Comparisons, detail::DenseMapPair<BoxAndHash, Box*>,
+                             /* MinSize= */ 8> DictMap;
 
     DictMap d;