Try to fix a bunch of compiler warnings on Win64.
diff --git a/PC/w9xpopen.c b/PC/w9xpopen.c
index f8439f2..b3978dd 100644
--- a/PC/w9xpopen.c
+++ b/PC/w9xpopen.c
@@ -30,7 +30,7 @@
     STARTUPINFO si;
     PROCESS_INFORMATION pi;
     DWORD exit_code=0;
-    int cmdlen = 0;
+    size_t cmdlen = 0;
     int i;
     char *cmdline, *cmdlinefill;