SDL_mixer: Fix include files for fork()

From 755fd6813b4cee73dec25bb5aaebbb8a027dd73f Mon Sep 17 00:00:00 2001
From: Dmitry Marakasov <[EMAIL REDACTED]>
Date: Wed, 20 Jul 2022 00:00:49 +0300
Subject: [PATCH] Fix include files for fork()

---
 CMakeLists.txt | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d73c2cea..f2d9d485 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -294,14 +294,14 @@ if(SDL2MIXER_CMD)
     target_compile_definitions(SDL2_mixer PRIVATE MUSIC_CMD)
     set(fork_found OFF)
     if(NOT fork_found)
-        check_symbol_exists(fork sys/unistd.h HAVE_FORK)
+        check_symbol_exists(fork unistd.h HAVE_FORK)
         if(HAVE_FORK)
             set(fork_found ON)
             target_compile_definitions(SDL2_mixer PRIVATE HAVE_FORK)
         endif()
     endif()
     if(NOT fork_found)
-        check_symbol_exists(fork sys/unistd.h HAVE_VFORK)
+        check_symbol_exists(fork unistd.h HAVE_VFORK)
         if(HAVE_VFORK)
             set(fork_found ON)
             target_compile_definitions(SDL2_mixer PRIVATE HAVE_VFORK)