Enable the threaded RTS when unregisterised too.

It was disabled by me in 1a470c94 (May
2007), but the commit gave no explanation as to why.  Perhaps this was before
we had a separate knob for GhcWithSMP.

Anyway, it looks like threaded works fine with unregisterised, so I'm
enabling it again.

mk/config.mk.in

@@ -263,12 +263,11 @@ ifeq "$(BootingFromHc)" "NO"
 GhcRTSWays += debug 
 endif
 
-# Want the threaded versions unless we're unregisterised
-# Defer the check until later by using $(if..), because GhcUnregisterised might
-# be set in build.mk, which hasn't been read yet.
-GhcRTSWays += $(if $(findstring NO, $(GhcUnregisterised)),thr thr_debug thr_l,)
-GhcRTSWays += $(if $(findstring p, $(GhcLibWays)),$(if $(findstring NO, $(GhcUnregisterised)),thr_p,),)
-GhcRTSWays += $(if $(findstring dyn, $(GhcLibWays)), dyn debug_dyn $(if $(findstring NO, $(GhcUnregisterised)),thr_dyn thr_debug_dyn),)
+# We always have the threaded versions, but note that SMP support may be disabled
+# (see GhcWithSMP).
+GhcRTSWays += thr thr_debug thr_l
+GhcRTSWays += $(if $(findstring p, $(GhcLibWays)),thr_p,)
+GhcRTSWays += $(if $(findstring dyn, $(GhcLibWays)),dyn debug_dyn thr_dyn thr_debug_dyn,)
 
 # We can only build GHCi threaded if we have a threaded RTS:
 GhcThreaded = $(if $(findstring thr,$(GhcRTSWays)),YES,NO)