Fix MinGW to us _snprintf in tgt-vvp/vvp_process.c

We need consistent pointer output (%p) and under MinGW we need to
us _snprintf instead of snprintf to get this. The recent event
control addition missed this. This has been reported to the MinGW
developers and they are working on a solution.

tgt-vvp/vvp_process.c

@@ -25,6 +25,10 @@
 #endif
 # include  <stdlib.h>
 
+#ifdef __MINGW32__ /* MinGW has inconsistent %p output. */
+#define snprintf _snprintf
+#endif
+
 static int show_statement(ivl_statement_t net, ivl_scope_t sscope);
 
 unsigned local_count = 0;