makepkg.sh.in: fix a GNU-ism in su invocation

GNU su supports the -c option to specify a command to execute.
However, other flavours of su may have a different interpretation
of the '-c' flag (e.g. FreeBSD and OpenBSD).

The behaviour is correct when '-c' follows an explicit username.

Signed-off-by: Rémy Oudompheng <remy@archlinux.org>
Signed-off-by: Allan McRae <allan@archlinux.org>
Signed-off-by: Dan McGee <dan@archlinux.org>

scripts/makepkg.sh.in

@@ -394,7 +394,7 @@ run_pacman() {
 		if [ "$(type -p sudo)" ]; then
 			cmd="sudo $cmd"
 		else
-			cmd="su -c '$cmd'"
+			cmd="su root -c '$cmd'"
 		fi
 	fi
 	eval "$cmd"