Fix missing include of <sys/wait.h>

Instead of relying on indirect includes, it's much cleaner if everybody
includes directly what he needs.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1419>
(cherry picked from commit ccfa7e9f2e)

hw/xfree86/os-support/xf86_OSlib.h

@@ -320,8 +320,6 @@ struct pcvtid {
 /* Generic                                                                */
 /**************************************************************************/
 
-#include <sys/wait.h>           /* May need to adjust this for other OSs */
-
 /* For PATH_MAX */
 #include "misc.h"
 

os/backtrace.c

@@ -27,9 +27,14 @@
 
 #include "os.h"
 #include "misc.h"
+
 #include <errno.h>
 #include <string.h>
 
+#ifndef WIN32
+#include <sys/wait.h>
+#endif
+
 #ifdef HAVE_LIBUNWIND
 
 #define UNW_LOCAL_ONLY