SDL_mixer: Add CYGWIN support for DLL library check

SDL Commits
1 
From d5dabfc3c700b636679e4c8ac17d5cd63b0c0ba0 Mon Sep 17 00:00:00 2001
From: Carlo Bramini <[EMAIL REDACTED]>
Date: Mon, 25 May 2026 15:32:06 +0200
Subject: [PATCH] Add CYGWIN support for DLL library check

(from https://github.com/libsdl-org/SDL_image/pull/747)
---
 cmake/PrivateSdlFunctions.cmake | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/cmake/PrivateSdlFunctions.cmake b/cmake/PrivateSdlFunctions.cmake
index 0f3eb406..afabcd73 100644
--- a/cmake/PrivateSdlFunctions.cmake
+++ b/cmake/PrivateSdlFunctions.cmake
@@ -199,7 +199,7 @@ function(target_get_dynamic_library DEST TARGET)
         endif()
         if(result)
             string(TOLOWER "${result}" result_lower)
-            if(WIN32 OR OS2)
+            if(WIN32 OR OS2 OR CYGWIN)
                 if(NOT result_lower MATCHES ".*dll")
                     message(FATAL_ERROR "\"${result}\" is not a .dll library")
                 endif()