Build system: fix 'make sdist'

This was broken in 4905b83a.

libraries/ghci/ghc.mk gets created by ./boot.

ghc.mk

@@ -1155,7 +1155,7 @@ SRC_DIST_TESTSUITE_TARBALL        = $(SRC_DIST_ROOT)/$(SRC_DIST_TESTSUITE_NAME).
 # Files to include in source distributions
 #
 SRC_DIST_GHC_DIRS = mk rules docs distrib bindisttest libffi includes \
-    utils docs rts compiler ghc driver libraries libffi-tarballs
+    utils docs rts compiler ghc driver libraries libffi-tarballs iserv
 SRC_DIST_GHC_FILES += \
     configure.ac config.guess config.sub configure \
     aclocal.m4 README.md ANNOUNCE HACKING.md INSTALL.md LICENSE Makefile \

libraries/ghci/ghc.mk

-libraries/ghci_PACKAGE = ghci
-libraries/ghci_dist-install_GROUP = libraries
-$(if $(filter ghci,$(PACKAGES_STAGE0)),$(eval $(call build-package,libraries/ghci,dist-boot,0)))
-$(if $(filter ghci,$(PACKAGES_STAGE1)),$(eval $(call build-package,libraries/ghci,dist-install,1)))
-$(if $(filter ghci,$(PACKAGES_STAGE2)),$(eval $(call build-package,libraries/ghci,dist-install,2)))