add nofooter by default when building the OpenCL specs (#1252)

This will minimize diffs in the future, especially for things like
the reference pages that may change infrequently.

Makefile

@@ -97,6 +97,7 @@ COMMONATTRIBOPTS = -a revdate="$(SPECDATE)" \
  -a stem=latexmath \
  -a generated=$(GENERATED) \
  -a sectnumlevels=5 \
+ -a nofooter \
  -a refprefix
 
 ATTRIBOPTS = -a revnumber="$(SPECREVISION)" \