Try a different conditional expression.

What's there works fine for me but mock doesn't like it for some reason.

cyrus-imapd.spec

@@ -404,7 +404,8 @@ find %buildroot -name ".packlist" -exec rm {} \;
 %ifnarch s390x ppc64
 make %{?_smp_mflags} check || exit 1
 
-%if %{with cassandane} && %__isa_bits == 64
+%if %{with cassandane}
+%if %__isa_bits == 64
 # Run the Cassandane test suite.  This will exhaustively test the various
 # server components, but running it in a mock chroot is rather an exercise.
 # Sadly Cassandane simply can't run on a 32-bit host at the moment.  It needs
@@ -486,6 +487,7 @@ export CYRUS_USER=$USER
 
 %endif
 %endif
+%endif
 
 
 %pre