process-debuginfo.in: rewrite module (de)compression logic

This change makes easier to add support of zstd-compressed modules in
the next commit.

scripts/process-debuginfo.in

@@ -23,12 +23,23 @@ strip_rel=
 if [ -z "${f#./lib/modules/*.ko}" ]; then
 	elfcompress=yes
 	strip_rel="--reloc-debug-sections"
-elif [ -z "${f#./lib/modules/*.ko.[gx]z}" ]; then
-	rezip=${f##*.}
-	rezip=${rezip/gz/gzip}
+elif [ -z "${f##./lib/modules/*.ko.*}" ]; then
+	ext=${f##*.}
+	unzip=
+	rezip=
+	case "$ext" in
+		gz)
+			unzip='gzip --force --decompress'
+			rezip='gzip --force --keep'
+			;;
+		xz)
+			unzip='xz --force --decompress'
+			rezip='xz --force --keep'
+			;;
+	esac
 	# Compressed module: uncompress it, and work with uncompressed one.
-	$rezip --decompress --force "$f"
-	f=${f%.[gx]z}
+	$unzip "$f"
+	f="${f%.*}"
 	elfcompress=yes
 	strip_rel="--reloc-debug-sections"
 elif [ -z "${f##./boot/vmlinuz-*}" ]; then