Fix permissions of package.cache when installing; fixes trac #5311

When we install the packages, ghc-pkg obeys umask when creating
package.cache, but for everything else we specify the permissions. We
therefore fix the permissions of package.cache afterwards.

ghc.mk

@@ -888,6 +888,10 @@ install_packages: libffi/package.conf.install rts/package.conf.install
 	    $(call make-command,                                           \
 	           "$(INSTALLED_GHC_PKG_REAL)"                             \
 	               --global-conf "$(INSTALLED_PACKAGE_CONF)" hide $p))
+# when we install the packages above, ghc-pkg obeys umask when creating
+# package.cache, but for everything else we specify the permissions. We
+# therefore now fix the permissions of package.cache
+	$(CREATE_DATA) '$(INSTALLED_PACKAGE_CONF)/package.cache'
 
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