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, 1 insertions, 0 deletions

diff --git a/dln.h b/dln.h
index d98b2607e2..9570de8f15 100644
--- a/dln.h
+++ b/dln.h
@@ -11,6 +11,7 @@
 
 #ifndef DLN_H
 #define DLN_H
+#include "ruby/defines.h"       /* for RUBY_SYMBOL_EXPORT_BEGIN */
 
 #ifdef __cplusplus
 # ifndef  HAVE_PROTOTYPES