makepkg: fix package arch detection

get_pkg_arch checked for the arch variable being overridden in the
package_$1() function when used with a package as a parameter.
However, when there was no override, it did not fall back to the
global value.

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

scripts/makepkg.sh.in

@@ -274,6 +274,7 @@ get_pkg_arch() {
 	else
 		local arch_override
 		eval $(declare -f package_$1 | sed -n 's/\(^[[:space:]]*arch=\)/arch_override=/p')
+		(( ${#arch_override[@]} == 0 )) && arch_override=("${arch[@]}")
 		if [[ $arch_override = "any" ]]; then
 			printf "%s\n" "any"
 		else