+# For each package P marked as "dph" or "extra" in $(TOP)/packages:
+# if $(TOP)/libraries/P exists, then
+# if $(TOP)/libraries/P/ghc-packages exists, then
+# * add each package from $(TOP)/libraries/P/ghc-packages2 to the list of
+# packages.
+# Note: ghc-packages2 might have a different list from
+# ghc-packages, this is to support dph which has some
+# packages that are automatically derived from a single
+# source by the build system).
+# * add $(TOP)/libraries/P to $(BUILD_DIRS)
+# This step is necessary in the case of dph, which has some
+# build system code in libraries/dph/ghc.mk, but
+# libraries/dph is not itself a package.
+# else
+# add P to the list of packages
+