Add missing GLAPIENTRY
diff --git a/src/mesa/main/api_loopback.c b/src/mesa/main/api_loopback.c
index c163d66..33e7ee8 100644
--- a/src/mesa/main/api_loopback.c
+++ b/src/mesa/main/api_loopback.c
@@ -218,7 +218,7 @@
 	   USHORT_TO_FLOAT(blue), USHORT_TO_FLOAT(alpha) );
 }
 
-static void
+static void GLAPIENTRY
 loopback_Color4ub_f( GLubyte red, GLubyte green, GLubyte blue, GLubyte alpha )
 {
    COLORF( UBYTE_TO_FLOAT(red), UBYTE_TO_FLOAT(green),