makepkg: use last match in BUILDENV/OPTIONS array

Using the last match in the BUILDENV and OPTIONS arrays allows the
user to easily override these values without specifying the entire
array. For example add "BUILDENV+=(sign)" in ~/.makepkg.conf.

Fixes FS#26701.

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

doc/makepkg.conf.5.txt

@@ -81,7 +81,8 @@ Options
 	This array contains options that affect the build environment, the defaults
 	are shown here. All options should always be left in the array; to enable
 	or disable an option simply remove or place an ``!'' at the front of the
-	option. Each works as follows:
+	option. If an option is specified multiple times, the final value takes
+	precedence. Each option works as follows:
 
 	*fakeroot*;;
 		Allow building packages as a non-root user. This is highly recommended.
@@ -134,7 +135,8 @@ Options
 	equivalent to options that can be placed in the PKGBUILD; the defaults are
 	shown here. All options should always be left in the array; to enable or
 	disable an option simply remove or place an ``!'' at the front of the
-	option. Each works as follows:
+	option. If an option is specified multiple times, the final value takes
+	precedence. Each option works as follows:
 
 	*strip*;;
 		Strip symbols from binaries and libraries. If you frequently use a

scripts/makepkg.sh.in

@@ -830,8 +830,9 @@ check_buildenv() {
 in_opt_array() {
 	local needle=$1; shift
 
-	local opt
-	for opt in "$@"; do
+	local i opt
+	for (( i = $#; i > 0; i-- )); do
+		opt=${!i}
 		if [[ $opt = "$needle" ]]; then
 			# enabled
 			return 0