Refactor package installation

There is now less makefile code duplication.
Also, stage2 packages are registered after GHC, which is important as
they might depend on the ghc package (as dph now does).

ghc.mk

@@ -816,6 +816,21 @@ endif
 INSTALLED_PACKAGES = $(filter-out haskeline mtl terminfo,$(PACKAGES))
 HIDDEN_PACKAGES = binary
 
+define set_INSTALL_DISTDIR
+# $1 = libraries/base, $2 = dist-install
+# =>
+# INSTALL_DISTDIR_libraries/base = dist-install
+INSTALL_DISTDIR_$1 = $2
+endef
+
+$(eval $(foreach p,$(INSTALLED_PACKAGES) $(PACKAGES_STAGE2),\
+$(call set_INSTALL_DISTDIR,libraries/$p,dist-install)))
+INSTALL_DISTDIR_compiler = stage2
+
+ALL_INSTALLED_PACKAGES = $(addprefix libraries/,$(INSTALLED_PACKAGES)) \
+                         compiler \
+                         $(addprefix libraries/,$(PACKAGES_STAGE2))
+
 install_packages: install_libexecs
 install_packages: libffi/package.conf.install rts/package.conf.install
 	$(INSTALL_DIR) $(DESTDIR)$(topdir)
@@ -823,24 +838,17 @@ install_packages: libffi/package.conf.install rts/package.conf.install
 	$(INSTALL_DIR) $(INSTALLED_PACKAGE_CONF)
 	"$(INSTALLED_GHC_PKG_REAL)" --force --global-conf $(INSTALLED_PACKAGE_CONF) update libffi/package.conf.install
 	"$(INSTALLED_GHC_PKG_REAL)" --force --global-conf $(INSTALLED_PACKAGE_CONF) update rts/package.conf.install
-	$(foreach p, $(INSTALLED_PACKAGES) $(PACKAGES_STAGE2),\
+	$(foreach p, $(ALL_INSTALLED_PACKAGES),\
 	    "$(GHC_CABAL_INPLACE)" install \
 		 $(INSTALLED_GHC_REAL) \
 		 $(INSTALLED_GHC_PKG_REAL) \
 		 $(DESTDIR)$(topdir) \
-		 libraries/$p dist-install \
+		 $p $(INSTALL_DISTDIR_$p) \
 		 '$(DESTDIR)' '$(prefix)' '$(ghclibdir)' '$(docdir)/html/libraries' \
 		 $(RelocatableBuild) &&) true
 	$(foreach p, $(HIDDEN_PACKAGES),\
 	    $(INSTALLED_GHC_PKG_REAL) --global-conf $(INSTALLED_PACKAGE_CONF) \
 	                              hide $p &&) true
-	"$(GHC_CABAL_INPLACE)" install \
-		 $(INSTALLED_GHC_REAL) \
-	 	 $(INSTALLED_GHC_PKG_REAL) \
-		 $(DESTDIR)$(topdir) \
-		 compiler stage2 \
-		 '$(DESTDIR)' '$(prefix)' '$(ghclibdir)' '$(docdir)/html/libraries' \
-		 $(RelocatableBuild)
 
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 # Binary distributions