SDL_mixer: upgrade vendored wavpack to 5.8.1 (be979)

From be9790f9d5455f55d684a68481010a0367fcce29 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Tue, 12 Aug 2025 00:28:50 +0300
Subject: [PATCH] upgrade vendored wavpack to 5.8.1

(cherry picked from commit d3428753ea90a3a48c439286bef18772a4ed2962)
---
 .gitmodules      | 2 +-
 external/wavpack | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/.gitmodules b/.gitmodules
index 6b7c2165..bbccdecd 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -33,7 +33,7 @@
 [submodule "external/wavpack"]
 	path = external/wavpack
 	url = https://github.com/libsdl-org/wavpack.git
-	branch = 5.7.0-sdl
+	branch = 5.8.1-SDL
 [submodule "external/libgme"]
 	path = external/libgme
 	url = https://github.com/libsdl-org/game-music-emu.git
diff --git a/external/wavpack b/external/wavpack
index 1258d38a..c9a53938 160000
--- a/external/wavpack
+++ b/external/wavpack
@@ -1 +1 @@
-Subproject commit 1258d38a2ccbed109980a8b7da73181498a5067a
+Subproject commit c9a5393829483f0bb72c1f0bea9042e82c5586e0