windows: use appropriate and portable format specifier for 64bit pointer

To print a 64bit poiner, fprintf() must be provided with the appropriate
format specifier.

The most portable in this case is PRIx64, which is redefined accordingly
on each platform. It comes from inttypes.h and it's the recommended way
to print a 64bit long hex value.

Fixes various warnings of this type:

event.c: In function ‘we_ctl’:
event.c:235:24: warning: 'I' flag used with ‘%x’ gnu_printf format
[-Wformat=]
  235 |     dmsg(D_EVENT_WAIT, "WE_CTL n=%d ev=%p rwflags=0x%04x arg="
ptr_format,
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
error.h:151:68: note: in definition of macro ‘dmsg’
  151 | #define dmsg(flags, ...) do { if (msg_test(flags)) {x_msg((flags),
__VA_ARGS__);} EXIT_FATAL(flags); } while (false)
      |
^~~~~~~~~~~
event.c:235:24: warning: format ‘%x’ expects argument of type ‘unsigned
int’, but argument 6 has type ‘long long unsigned int’ [-Wformat=]
  235 |     dmsg(D_EVENT_WAIT, "WE_CTL n=%d ev=%p rwflags=0x%04x arg="
ptr_format,
      |                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
......
  239 |          (ptr_type)arg);
      |          ~~~~~~~~~~~~~
      |          |
      |          long long unsigned int

Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <20210501130640.9330-2-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22268.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>

src/openvpn/common.h

@@ -44,7 +44,7 @@ typedef int interval_t;
  * Printf formats for special types
  */
 #ifdef _WIN64
-#define ptr_format              "0x%I64x"
+#define ptr_format              "0x%016" PRIx64
 #else
 #define ptr_format              "0x%08lx"
 #endif