decouple internal.h headers

Saves comitters' daily life by avoid #include-ing everything from
internal.h to make each file do so instead.  This would significantly
speed up incremental builds.

We take the following inclusion order in this changeset:

1.  "ruby/config.h", where _GNU_SOURCE is defined (must be the very
    first thing among everything).
2.  RUBY_EXTCONF_H if any.
3.  Standard C headers, sorted alphabetically.
4.  Other system headers, maybe guarded by #ifdef
5.  Everything else, sorted alphabetically.

Exceptions are those win32-related headers, which tend not be self-
containing (headers have inclusion order dependencies).

1 files changed, 8 insertions, 2 deletions

diff --git a/internal/hash.h b/internal/hash.h
index 634092e4c2..90a27fd189 100644
--- a/internal/hash.h
+++ b/internal/hash.h
@@ -55,8 +55,14 @@ struct RHash {
 };
 
 #define RHASH(obj) (R_CAST(RHash)(obj))
-#undef RHASH_IFNONE
-#undef RHASH_SIZE
+
+#ifdef RHASH_IFNONE
+# undef RHASH_IFNONE
+#endif
+
+#ifdef RHASH_SIZE
+# undef RHASH_SIZE
+#endif
 
 /* hash.c */
 void rb_hash_st_table_set(VALUE hash, st_table *st);