SDL: Use posix_spawn() on QNX

SDL Commits
1 
From 60d95e2a7777397498f6a9651d34358170b605e1 Mon Sep 17 00:00:00 2001
From: Elad Lahav <[EMAIL REDACTED]>
Date: Tue, 10 Jan 2023 07:08:51 -0500
Subject: [PATCH] Use posix_spawn() on QNX

---
 CMakeLists.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0f2bf8a227a5..64ce5318822b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1822,6 +1822,7 @@ elseif(UNIX AND NOT APPLE AND NOT RISCOS AND NOT HAIKU)
     # specifier (on purpose), but SDL expects "(null)". Use the built-in
     # implementation.
     set (HAVE_VSNPRINTF 0)
+    set (USE_POSIX_SPAWN 1)
   endif()
 elseif(WINDOWS)
   find_program(WINDRES windres)