Revert "Use atomics for protected-ints on other *nixes too (not just FreeBSD)"

This reverts commit e1e034cc.

Didn't work for .cpp files:
stdatomic.h:40:9: error: ‘_Atomic’ does not name a type
typedef _Atomic _Bool atomic_bool

src/xpdev/threadwrap.c

@@ -217,7 +217,7 @@ int DLLCALL pthread_mutex_destroy(pthread_mutex_t* mutex)
 /* Protected (thread-safe) Integers (e.g. atomic/interlocked variables) */
 /************************************************************************/
 
-#ifdef __unix__
+#ifdef __FreeBSD__
 #define PROTECTED_TYPE_INIT(type) \
 int DLLCALL protected_##type##_init(protected_##type##_t* prot, type##_t value) \
 { \

src/xpdev/threadwrap.h

@@ -40,7 +40,7 @@
 #include "gen_defs.h"	/* HANDLE */
 #include "wrapdll.h"	/* DLLEXPORT and DLLCALL */
 
-#ifdef __unix__
+#ifdef __FreeBSD__
 #include <stdatomic.h>
 #endif
 
@@ -152,7 +152,7 @@ DLLEXPORT int DLLCALL pthread_once(pthread_once_t *oc, void (*init)(void));
 /* working and being thread-safe on all platforms that support pthread	*/
 /* mutexes.																*/
 /************************************************************************/
-#ifdef __unix__
+#ifdef __FreeBSD__
 typedef _Atomic(int32_t) protected_int32_t;
 typedef _Atomic(uint32_t) protected_uint32_t;
 typedef _Atomic(int64_t) protected_int64_t;