+# Handy way to test whether we're building shared libs or not.
+BuildSharedLibs=$(strip $(if $(findstring dyn,$(GhcLibWays)),YES,NO))
+
+# In addition, the RTS is built in some further variations. Ways that
+# make sense here:
+#
+# thr : threaded
+# thr_p : threaded profiled
+# debug : debugging (compile with -g for the C compiler, and -DDEBUG)
+# debug_p : debugging profiled
+# thr_debug : debugging threaded
+# thr_debug_p : debugging threaded profiled
+# t : ticky-ticky profiling
+# debug_t : debugging ticky-ticky profiling
+# l : event logging
+# thr_l : threaded and event logging
+#
+GhcRTSWays=l
+
+# Usually want the debug version
+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 can only build GHCi threaded if we have a threaded RTS:
+GhcThreaded = $(if $(findstring thr,$(GhcRTSWays)),YES,NO)
+