This patch is required when using ghc 6.4, which complains about
multiple Main modules when generating dependencies with ghc -M.

Index: ghc.mk
===================================================================
--- ghc.mk	(revision 1741)
+++ ghc.mk	(working copy)
@@ -36,7 +36,10 @@
 # compute the dependencies
 # NB: ./ prefixes stripped from dependencies for proper operation with BSD make
 depend-dir: $(mach_SRCS) $(cycc_SRCS) $(cymk_SRCS) $(newer_SRCS)
-	$(HC) $(HCFLAGS) $(GHC_HCFLAGS) -M -optdep-f -optdep.depend.ghc \
-		$(mach_SRCS) $(cycc_SRCS) $(cymk_SRCS) $(newer_SRCS)
-	sed 's,\./,,' .depend.ghc > .depend
-	@rm -f -- .depend.ghc .depend.ghc.bak
+	$(HC) $(HCFLAGS) $(GHC_HCFLAGS) -M -optdep-f -optdep.depend.mach $(mach_SRCS)
+	$(HC) $(HCFLAGS) $(GHC_HCFLAGS) -M -optdep-f -optdep.depend.cycc $(cycc_SRCS)
+	$(HC) $(HCFLAGS) $(GHC_HCFLAGS) -M -optdep-f -optdep.depend.cymk $(cymk_SRCS)
+	$(HC) $(HCFLAGS) $(GHC_HCFLAGS) -M -optdep-f -optdep.depend.newer $(newer_SRCS)
+	sed 's,\./,,' .depend.mach .depend.cycc .depend.cymk .depend.newer > .depend
+	@rm -f -- .depend.mach .depend.cycc .depend.cymk .depend.newer
+	@rm -f -- .depend.mach.bak .depend.cycc.bak .depend.cymk.bak .depend.newer.bak