Update sync-all and others files w.r.t. merged testsuite (re Trac #8545)
See merge commit 66693401b98cb5aa912948af7bbd2182474f50c4
This commit also adds a check for a left-over testsuite/.git folder to sync-all
This way, the first time sync-all is called after updating to a
post-testsuite-merge (see Trac #8545) state of ghc.git, the sync-all script
aborts with an error message if a testsuite/.git folder is detected and
thus forces the user to take action.
Signed-off-by: Herbert Valerio Riedel <email@example.com>