Bug#944493: Please disable parallel install

[Florian Weimer]

Package: src:ghc
Version: 8.8.1+dfsg1+is+8.6.5+dfsg1-2

Something like this seems to be needed because the install target does
not ensure that directories are created before files that are
installed into them:

diff -Nru ghc-8.8.1+dfsg1+is+8.6.5+dfsg1/debian/rules ghc-8.8.1+dfsg1+is+8.6.5+dfsg1/debian/rules
--- ghc-8.8.1+dfsg1+is+8.6.5+dfsg1/debian/rules	2019-09-21 12:06:31.000000000 +0200
+++ ghc-8.8.1+dfsg1+is+8.6.5+dfsg1/debian/rules	2019-11-10 19:03:00.000000000 +0100
@@ -174,7 +174,7 @@
 PROF_FILE = \( -name "*.p_*" -o -name "lib*_p.a" \)
 
 override_dh_auto_install:
-	dh_auto_install
+	dh_auto_install --no-parallel
 
 	# Delete all the library LICENSE files
 	rm -f debian/tmp/usr/share/doc/ghc-doc/html/libraries/*/LICENSE

I saw a build failure due to a missing debian/tmp/usr/bin directory
when symlinking haddock, and after the change above, it was gone.