added __PHYSFS_ATOMIC_INCR and __PHYSFS_ATOMIC_DECR for watcom compiler

src/physfs_internal.h

@@ -117,6 +117,15 @@ __PHYSFS_COMPILE_TIME_ASSERT(LongEqualsInt, sizeof (int) == sizeof (long));
 #elif defined(__clang__) || (defined(__GNUC__) && (((__GNUC__ * 10000) + (__GNUC_MINOR__ * 100)) >= 40100))
 #define __PHYSFS_ATOMIC_INCR(ptrval) __sync_fetch_and_add(ptrval, 1)
 #define __PHYSFS_ATOMIC_DECR(ptrval) __sync_fetch_and_add(ptrval, -1)
+#elif defined(__WATCOMC__) && defined(__386__)
+extern __inline int _xadd_watcom(volatile int *a, int v);
+#pragma aux _xadd_watcom = \
+  "lock xadd [ecx], eax" \
+  parm [ecx] [eax] \
+  value [eax] \
+  modify exact [eax];
+#define __PHYSFS_ATOMIC_INCR(ptrval) _xadd_watcom(ptrval, 1)
+#define __PHYSFS_ATOMIC_DECR(ptrval) _xadd_watcom(ptrval, -1)
 #else
 #define PHYSFS_NEED_ATOMIC_OP_FALLBACK 1
 int __PHYSFS_ATOMIC_INCR(int *ptrval);