Swap isomorphism subjects

In this order it becomes possible to use VCL_VOID transparently as void
without having to declare it again as a typedef. It doesn't matter for
VRT_CTX because it tends to be easier to use it instead of its actual
C type (with the typedef-in-patch penalty).

Wave in my general direction if you're not slink and yet can make sense
of the previous paragraph.

tools/coccinelle/varnish.iso

@@ -25,11 +25,11 @@ Type
 type VCL_VOID;
 @@
 
-VCL_VOID <=> void
+void <=> VCL_VOID
 
 Type
 @ vcl_bool @
 type VCL_BOOL;
 @@
 
-VCL_BOOL <=> unsigned
+unsigned <=> VCL_BOOL