compat/atomics: add typecasts in atomic_compare_exchange_strong()

The Solaris and Windows emulations of atomic_compare_exchange_strong()
need typecasts to avoid compiler warnings, because the functions they
call expect a void* pointer but an intptr_t integer is passed.

Note that the emulations of atomic_compare_exchange_strong() (except
the gcc version) only work for atomic_intptr_t because of the type of
the second argument (|expected|). See
http://en.cppreference.com/w/c/atomic:

_Bool atomic_compare_exchange_strong( volatile A* obj,
                                      C* expected, C desired );

The types of the first argument and second argument are different
(|A| and |C|, respectively). |C| is the non-atomic type corresponding
to |A|. In the emulations of atomic_compare_exchange_strong(), |C| is
intptr_t. This implies |A| can only be sig_intptr_t.
Signed-off-by: Wan-Teh Chang <wtc@google.com>

compat/atomics/suncc/stdatomic.h

@@ -108,7 +108,7 @@ static inline int atomic_compare_exchange_strong(intptr_t *object, intptr_t *exp
                                                  intptr_t desired)
 {
     intptr_t  old = *expected;
-    *expected = atomic_cas_ptr(object, old, desired);
+    *expected = (intptr_t)atomic_cas_ptr(object, (void *)old, (void *)desired);
     return *expected == old;
 }
 

compat/atomics/win32/stdatomic.h

@@ -104,7 +104,8 @@ static inline int atomic_compare_exchange_strong(intptr_t *object, intptr_t *exp
                                                  intptr_t desired)
 {
     intptr_t old = *expected;
-    *expected = InterlockedCompareExchangePointer(object, desired, old);
+    *expected = (intptr_t)InterlockedCompareExchangePointer(
+        (PVOID *)object, (PVOID)desired, (PVOID)old);
     return *expected == old;
 }