Add MRB_SYM() for inline symbols.

include/mruby/hash.h

@@ -201,7 +201,7 @@ MRB_API void mrb_hash_merge(mrb_state *mrb, mrb_value hash1, mrb_value hash2);
 /* RHASH_TBL allocates st_table if not available. */
 #define RHASH(obj)   ((struct RHash*)(mrb_ptr(obj)))
 #define RHASH_TBL(h)          (RHASH(h)->ht)
-#define RHASH_IFNONE(h)       mrb_iv_get(mrb, (h), mrb_intern_lit(mrb, "ifnone"))
+#define RHASH_IFNONE(h)       mrb_iv_get(mrb, (h), MRB_SYM(ifnone))
 #define RHASH_PROCDEFAULT(h)  RHASH_IFNONE(h)
 
 #define MRB_HASH_DEFAULT      1

include/mruby/presym.h

@@ -0,0 +1,19 @@
+/**
+** @file mruby/presym.h - Preallocated Symbols
+**
+** See Copyright Notice in mruby.h
+*/
+
+#ifndef MRUBY_PRESYM_H
+#define MRUBY_PRESYM_H
+
+#undef MRB_PRESYM_MAX
+#define MRB_PRESYM_CSYM(sym, num) MRB_PRESYM__##sym = (num<<1),
+#define MRB_PRESYM_SYM(sym, num)
+
+enum mruby_presym {
+#include <../build/presym.inc>
+};
+
+#define MRB_SYM(sym) MRB_PRESYM__##sym
+#endif  /* MRUBY_PRESYM_H */