rb_io_buffer_t: fix packing on gcc

* include/ruby/io.h (rb_io_buffer_t): fix packing on gcc
  r46892 caused packing to be a no-op on gcc (4.7.2-5, Debian)
  [Bug #10079][ruby-core:63912]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46894 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,9 @@
+Tue Jul 22 01:48:38 2014  Eric Wong  <e@80x24.org>
+
+	* include/ruby/io.h (rb_io_buffer_t): fix packing on gcc
+	  r46892 caused packing to be a no-op on gcc (4.7.2-5, Debian)
+	  [Bug #10079][ruby-core:63912]
+
 Mon Jul 21 15:55:42 2014  fuji70  <fujifuji70@gmail.com>
 
 	* lib/optparse.rb (getopts): print default values and descriptions

include/ruby/io.h

@@ -51,12 +51,13 @@ extern "C" {
 
 RUBY_SYMBOL_EXPORT_BEGIN
 
-PACKED_STRUCT(typedef struct {
+PACKED_STRUCT(struct rb_io_buffer_t {
     char *ptr;                  /* off + len <= capa */
     int off;
     int len;
     int capa;
-} rb_io_buffer_t);
+});
+typedef struct rb_io_buffer_t rb_io_buffer_t;
 
 typedef struct rb_io_t {
     FILE *stdio_file;		/* stdio ptr for read/write if available */