sdl2-compat: Make X11 dependency required on UNIX platforms

From 1ddf479f95b9958512301027240c7e5427418da6 Mon Sep 17 00:00:00 2001
From: Marcin Serwin <[EMAIL REDACTED]>
Date: Wed, 7 May 2025 20:52:30 +0200
Subject: [PATCH] Make X11 dependency required on UNIX platforms

The X11 headers are included in sdl2_compat.h so building without them installed in the standard location fails with:

In file included from /build/source/src/dynapi/SDL_dynapi.c:23:
/build/source/src/dynapi/../sdl2_compat.h:1289:10: fatal error: X11/Xlib.h: No such file or directory
1289 | #include <X11/Xlib.h>
| ^~~~~~~~~~~~
compilation terminated.

---
 CMakeLists.txt | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 89bf07e..af58151 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -223,15 +223,16 @@ set(SDL2COMPAT_SRCS
   src/dynapi/SDL_dynapi.c
 )
 
+if(UNIX AND NOT ANDROID)
+  find_package(X11 REQUIRED)
+  include_directories(${X11_INCLUDE_DIR})
+endif()
+
 if(APPLE)
   list(APPEND SDL2COMPAT_SRCS
     "src/sdl2_compat_objc.m"
   )
 
-  find_package(X11)
-  if(X11_FOUND)
-    include_directories("${X11_INCLUDE_DIR}")
-  endif()
   if(POLICY CMP0068)
     cmake_policy(SET CMP0068 NEW)  # on macOS, don't let RPATH affect install_name.
   endif()