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, 12 insertions, 3 deletions

diff --git a/symbol.c b/symbol.c
index 14517df01e..a0aa4cc75f 100644
--- a/symbol.c
+++ b/symbol.c
@@ -9,13 +9,22 @@
 
 **********************************************************************/
 
+#include "gc.h"
+#include "internal.h"
+#include "internal/error.h"
+#include "internal/gc.h"
+#include "internal/hash.h"
+#include "internal/object.h"
+#include "internal/symbol.h"
+#include "internal/vm.h"
+#include "probes.h"
 #include "ruby/encoding.h"
 #include "ruby/st.h"
-#include "internal.h"
 #include "symbol.h"
-#include "gc.h"
-#include "probes.h"
 
+#ifndef USE_SYMBOL_GC
+# define USE_SYMBOL_GC 1
+#endif
 #ifndef SYMBOL_DEBUG
 # define SYMBOL_DEBUG 0
 #endif