[perl-Cairo] Fix compilation against perl 5.15.3

[Torsten SchÃnfeld <tsch src gnome org>]

commit d41fa916660aebfaef418b6879ce3d42361115dd
Author: Torsten SchÃnfeld <kaffeetisch gmx de>
Date:   Tue Aug 16 19:44:31 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.

 Cairo.xs |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)
---
diff --git a/Cairo.xs b/Cairo.xs
index ac78b68..7e35f4a 100644
--- a/Cairo.xs
+++ b/Cairo.xs
@@ -24,9 +24,12 @@ call_xs (pTHX_ void (*subaddr) (pTHX_ CV *), CV * cv, SV ** mark)
 	PUTBACK;	/* forget return values */
 }
 
+#ifndef XS_EXTERNAL
+# define XS_EXTERNAL(name) XS(name)
+#endif
 #define CAIRO_PERL_CALL_BOOT(name)				\
 	{							\
-		extern XS(name);				\
+		extern XS_EXTERNAL (name);			\
 		call_xs (aTHX_ name, cv, mark);	\
 	}