[perl-Glib] Fix compilation against perl 5.15.3

[Torsten SchÃnfeld <tsch src gnome org>]

commit 2c335fb864b0848316e053e5feb0ac00bdfd70d3
Author: Torsten SchÃnfeld <kaffeetisch gmx de>
Date:   Tue Aug 16 20:54:17 2011 +0200

    Fix compilation against perl 5.15.3
    
    This version of perl redefined the XS macro to include "static", which collides
    with the "extern" we use at one point.  Switch to XS_EXTERNAL instead.

 gperl.h |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/gperl.h b/gperl.h
index 01e48ac..b76e276 100644
--- a/gperl.h
+++ b/gperl.h
@@ -387,9 +387,12 @@ void _gperl_call_XS (pTHX_ void (*subaddr) (pTHX_ CV *), CV * cv, SV ** mark);
  * exported to perl.  if the file has MODULE = Foo::Bar, the boot symbol
  * would be boot_Foo__Bar.
  */
+#ifndef XS_EXTERNAL
+# define XS_EXTERNAL(name) XS(name)
+#endif
 #define GPERL_CALL_BOOT(name)	\
 	{						\
-		extern XS(name);			\
+		extern XS_EXTERNAL (name);		\
 		_gperl_call_XS (aTHX_ name, cv, mark);	\
 	}