Ensure nested CPR does not break havoc with repeat

...not that we do have nested CPR right now, but when we do, this should
better not break.

testsuite/tests/cpranal/should_run/CPRRepeat.hs

+repeat' :: x -> [x]
+repeat' x = x : repeat' x
+
+main = print (repeat' () !! 10 )

testsuite/tests/cpranal/should_run/CPRRepeat.stdout

+()

testsuite/tests/cpranal/should_run/Makefile

+TOP=../../..
+include $(TOP)/mk/boilerplate.mk
+include $(TOP)/mk/test.mk

testsuite/tests/cpranal/should_run/all.T

+# Just do the opt way...
+def f( name, opts ):
+  opts.only_ways = ['optasm']
+
+setTestOpts(f)
+
+test('CPRRepeat', normal, compile_and_run, [''])