SDL_mixer: Fix issue finding libxmp dependency

SDL Commits
1 
From 831a83fd4a9f73d8855c2e737b02c2e83d5a9ba2 Mon Sep 17 00:00:00 2001
From: Francisco Javier Trujillo Mata <[EMAIL REDACTED]>
Date: Mon, 8 Aug 2022 17:33:21 +0200
Subject: [PATCH] Fix issue finding libxmp dependency

cmake/Findlibxmp.cmake and cmake/Findlibxmp-lite.cmake were missing an include for FindPackageHandleStandardArgs.
---
 cmake/Findlibxmp-lite.cmake | 2 ++
 cmake/Findlibxmp.cmake      | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/cmake/Findlibxmp-lite.cmake b/cmake/Findlibxmp-lite.cmake
index d0b2bbbb..4df1cdaf 100644
--- a/cmake/Findlibxmp-lite.cmake
+++ b/cmake/Findlibxmp-lite.cmake
@@ -1,3 +1,5 @@
+include(FindPackageHandleStandardArgs)
+
 find_library(libxmp_lite_LIBRARY
     NAMES xmp
 )
diff --git a/cmake/Findlibxmp.cmake b/cmake/Findlibxmp.cmake
index c2c44882..e81d0fa0 100644
--- a/cmake/Findlibxmp.cmake
+++ b/cmake/Findlibxmp.cmake
@@ -1,3 +1,5 @@
+include(FindPackageHandleStandardArgs)
+
 find_library(libxmp_LIBRARY
     NAMES xmp
 )