atomics: Fix the win32 atomic_exchange function

This fixes building with MSVC after
a2a38b1606.

Remove the stray semicolon, and add casts for the input argument
(which is an intptr_t*) to the right type (PVOID volatile *).

Signed-off-by: Martin Storsjö <martin@martin.st>

compat/atomics/win32/stdatomic.h

@@ -96,7 +96,7 @@ do {                                    \
     atomic_load(object)
 
 #define atomic_exchange(object, desired) \
-    InterlockedExchangePointer(object, desired);
+    InterlockedExchangePointer((PVOID volatile *)object, (PVOID)desired)
 
 #define atomic_exchange_explicit(object, desired, order) \
     atomic_exchange(object, desired)