Add a haddock target, for just building the haddock docs

ghc.mk

@@ -100,6 +100,8 @@
 #           o libraries/*
 #           o compiler
 
+.PHONY: default all haddock
+
 default : all
 
 # Just bring makefiles up to date:

rules/haddock.mk

@@ -21,6 +21,8 @@ else
 $$(error Already got a haddock file for $$($1_PACKAGE))
 endif
 
+haddock: $$($$($1_PACKAGE)_HADDOCK_FILE)
+
 ifeq "$$(HADDOCK_DOCS)" "YES"
 $(call all-target,$1_$2_haddock,$$($$($1_PACKAGE)_HADDOCK_FILE))
 endif