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, 9 insertions, 2 deletions

diff --git a/struct.c b/struct.c
index d1aa7c278f..79131db2bd 100644
--- a/struct.c
+++ b/struct.c
@@ -9,10 +9,17 @@
 
 **********************************************************************/
 
-#include "internal.h"
-#include "vm_core.h"
 #include "id.h"
+#include "internal.h"
+#include "internal/class.h"
+#include "internal/error.h"
+#include "internal/hash.h"
+#include "internal/object.h"
+#include "internal/proc.h"
+#include "internal/struct.h"
+#include "internal/symbol.h"
 #include "transient_heap.h"
+#include "vm_core.h"
 
 /* only for struct[:field] access */
 enum {