makepkg: implement locking for pacman commands

When pacman is run as root to do -S, -U, or -R, it would immediately
abort if pacman is not ready for use. Instead, poll the lockfile and
wait until it becomes available.

Implements FS#28840

Original-patch-by: Georges Dubus <georges.dubus@compiletoi.net>
Signed-off-by: Eli Schwartz <eschwartz@archlinux.org>
Signed-off-by: Allan McRae <allan@archlinux.org>

scripts/makepkg.sh.in

@@ -228,6 +228,15 @@ run_pacman() {
 		else
 			cmd=(su root -c "$(printf '%q ' "${cmd[@]}")")
 		fi
+		local lockfile="$(pacman-conf DBPath)/db.lck"
+		while [[ -f $lockfile ]]; do
+			local timer=0
+			msg "$(gettext "Pacman is currently in use, please wait...")"
+			while [[ -f $lockfile ]] && (( timer < 10 )); do
+				(( ++timer ))
+				sleep 3
+			done
+		done
 	fi
 	"${cmd[@]}"
 }