Ensure package.cache is newer than registration files after make install

Rebuild package.cache to ensure that it's newer than the package
database registration files, avoiding out-of-date cache warnings from
ghc-pkg. See #13375.

Test Plan: `make install`, run `ghc-pkg list`, look for out-of-date
cache warning

Reviewers: austin

Subscribers: rwbarton, thomie

GHC Trac Issues: #13375

Differential Revision: https://phabricator.haskell.org/D3569

ghc.mk

@@ -1027,6 +1027,10 @@ install_packages: rts/dist/package.conf.install
 # with an 077 umask.
 	for f in '$(INSTALLED_PACKAGE_CONF)'/*; do $(CREATE_DATA) "$$f"; done
 
+# Finally, update package.cache to ensure it's newer than the registration
+# files. This avoids #13375.
+	$(INSTALLED_GHC_PKG_REAL) --global-package-db "$(INSTALLED_PACKAGE_CONF)" recache
+
 # -----------------------------------------------------------------------------
 # Binary distributions