Fix GLAPIENTRYP for OS X.

Fix build problems related to incorrect define of GLAPIENTRYP on OS X.
Reported by bushing on IRC.
diff --git a/src/mesa/glapi/gl_table.py b/src/mesa/glapi/gl_table.py
index 52b4be1..69f7bd7 100644
--- a/src/mesa/glapi/gl_table.py
+++ b/src/mesa/glapi/gl_table.py
@@ -49,7 +49,11 @@
 
 	def printRealHeader(self):
 		print '#ifndef GLAPIENTRYP'
-		print '#define GLAPIENTRYP'
+		print '# ifndef GLAPIENTRY'
+		print '#  define GLAPIENTRY'
+		print '# endif'
+		print ''
+		print '# define GLAPIENTRYP GLAPIENTRY *'
 		print '#endif'
 		print ''
 		print 'typedef void (*_glapi_proc)(void); /* generic function pointer */'