Windows: Don't define or check for WIN32.

_WIN32 is defined by the compiler, and is arguably a more reliable
test that WIN32. Switch to checking for _WIN32 in a couple of places in
the code.

Remove a WIN32 definition from config.h. It was added for the WinPcap
developer pack but we no longer use that.

cmakeconfig.h.in

@@ -316,11 +316,6 @@
 #endif
 
 #if defined(_WIN32)
-   /* WpdPack/INclude/pcap/pcap.h checks for "#if defined(WIN32)" */
-#  ifndef WIN32
-#    define WIN32	1
-#  endif
-
    /*
     * Flex (v 2.5.35) uses this symbol to "exclude" unistd.h
     */

speexdsp/stack_alloc.h

@@ -36,7 +36,7 @@
 #define STACK_ALLOC_H
 
 #ifdef USE_ALLOCA
-# ifdef WIN32
+# ifdef _WIN32
 #  include <malloc.h>
 # else
 #  ifdef HAVE_ALLOCA_H

ui/help_url.c

@@ -31,7 +31,7 @@ gchar *
 user_guide_url(const gchar *page) {
     GString *url = g_string_new("");
 
-#if defined(WIN32)
+#if defined(_WIN32)
     /*
      * The User's Guide is in a directory named "Wireshark User's Guide" in
      * the program directory.
@@ -48,7 +48,7 @@ user_guide_url(const gchar *page) {
         /* try to open the HTML page from wireshark.org instead */
         g_string_printf(url, "file://" DOC_DIR "/guides/wsug_html_chunked/%s", page);
     }
-#endif /* WIN32 / DOC_DIR */
+#endif /* _WIN32 / DOC_DIR */
 
 
     /* Fall back to wireshark.org. */