Problem: MS VC++ build broken

Solution: try to detect architecture if building with VC++ and
hardcode pointer size accordingly.
Expressions are not allowed inside declspec intrinsics, which
includes other intrinsics.

include/zmq.h

@@ -238,8 +238,10 @@ typedef struct zmq_msg_t {
         (defined (__SUNPRO_C) && __SUNPRO_C >= 0x590) || \
         (defined (__SUNPRO_CC) && __SUNPRO_CC >= 0x590)
     unsigned char _ [64] __attribute__ ((aligned (sizeof (void *))));
-#elif defined(_MSC_VER)
-    __declspec (align (sizeof (void *))) unsigned char _ [64];
+#elif defined (_MSC_VER) && (defined (_M_X64) || defined (_M_ARM64))
+    __declspec (align (8)) unsigned char _ [64];
+#elif defined (_MSC_VER) && (defined (_M_IX86) || defined (_M_ARM_ARMV7VE))
+    __declspec (align (4)) unsigned char _ [64];
 #else
     unsigned char _ [64];
 #endif