-# a pretty strong internal check
-GhcHcOpts=-O -Rghc-timing
-
-# GhcWithHscBuiltViaC - build GHC compiler proper (\`hsc') from .hc files?
-GhcWithHscBuiltViaC=@BootingFromHc@
+# a pretty strong internal check of the compiler being
+# used to compile GHC. Useful when bootstrapping.
+GhcHcOpts=-Rghc-timing
+
+# Extra options added to specific stages of the compiler bootstrap.
+# These are placed later on the command line, and may therefore
+# override options from $(GhcHcOpts).
+GhcStage1HcOpts=
+GhcStage2HcOpts=
+GhcStage3HcOpts=
+
+# Build a compiler that will build *unregisterised* libraries and
+# binaries by default. Unregisterised code is supposed to compile and
+# run without any support for architecture-specific assembly mangling,
+# register assignment or tail-calls, and is therefore a good way to get
+# started when porting GHC to new architectures.
+#
+# If this is set to NO, you can still use the unregisterised way
+# (way 'u') to get unregisterised code, but the default way will be
+# registerised.
+#
+# NOTE: this is not the same as building the compiler itself
+# unregisterised. That's done by either (a) bootstrapping with a
+# compiler that was built with GhcUnregisterised=YES, or (b)
+# bootstrapping with a compiler that has way 'u' libraries, and the
+# flag '-unreg' is added to GhcHcOpts above.
+#
+GhcUnregisterised=NO