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, 7 insertions, 2 deletions

diff --git a/internal/class.h b/internal/class.h
index 254094e038..72d3b9ea54 100644
--- a/internal/class.h
+++ b/internal/class.h
@@ -16,8 +16,13 @@
 #include "ruby/intern.h"        /* for rb_alloc_func_t */
 #include "ruby/ruby.h"          /* for struct RBasic */
 
-#undef RClass /* See also include/ruby/backward.h */
-#undef RCLASS_SUPER
+#ifdef RClass
+# undef RClass /* See also include/ruby/backward.h */
+#endif
+
+#ifdef RCLASS_SUPER
+# undef RCLASS_SUPER
+#endif
 
 struct rb_deprecated_classext_struct {
     char conflict[sizeof(VALUE) * 3];