makepkg: correctly add changelog files

Before this, we'd see bizzare behavior of:

  -> Adding changelog file (systemd.install)...

And, changelog files in the global section would not be added at all.

The code is clearly wrong here, as it references 'install' within a
loop of 'changelog' and 'install'. Let's use parameter indirection to
ensure that the proper file is identified and added.

Signed-off-by: Allan McRae <allan@archlinux.org>

scripts/makepkg.sh.in

@@ -2367,7 +2367,7 @@ create_srcpackage() {
 	for i in 'changelog' 'install'; do
 		local file files
 
-		[[ $install ]] && files+=("$install")
+		[[ ${!i} ]] && files+=("${!i}")
 		for name in "${pkgname[@]}"; do
 			if extract_function_var "package_$name" "$i" 0 file; then
 				files+=("$file")