windows: use built-in _WIN32 macro to detect Windows

Windows compilers define `_WIN32` automatically. Windows SDK headers
or build env defines `WIN32`, or we have to take care of it. The
agreement seems to be that `_WIN32` is the preferred practice here.
Make the source code rely on that to detect we're building for Windows.

Public `curl.h` was using `WIN32`, `__WIN32__` and `CURL_WIN32` for
Windows detection, next to the official `_WIN32`. After this patch it
only uses `_WIN32` for this. Also, make it stop defining `CURL_WIN32`.

There is a slight chance these break compatibility with Windows
compilers that fail to define `_WIN32`. I'm not aware of any obsolete
or modern compiler affected, but in case there is one, one possible
solution is to define this macro manually.

grepping for `WIN32` remains useful to discover Windows-specific code.

Also:

- extend `checksrc` to ensure we're not using `WIN32` anymore.

- apply minor formatting here and there.

- delete unnecessary checks for `!MSDOS` when `_WIN32` is present.

Co-authored-by: Jay Satiro
Reviewed-by: Daniel Stenberg

Closes #12376

tests/server/getpart.c

@@ -60,7 +60,7 @@ curl_free_callback Curl_cfree = (curl_free_callback)free;
 curl_realloc_callback Curl_crealloc = (curl_realloc_callback)realloc;
 curl_strdup_callback Curl_cstrdup = (curl_strdup_callback)strdup;
 curl_calloc_callback Curl_ccalloc = (curl_calloc_callback)calloc;
-#if defined(WIN32) && defined(UNICODE)
+#if defined(_WIN32) && defined(UNICODE)
 curl_wcsdup_callback Curl_cwcsdup = (curl_wcsdup_callback)_wcsdup;
 #endif
 

tests/server/mqttd.c

@@ -1016,7 +1016,7 @@ int main(int argc, char *argv[])
   msnprintf(loglockfile, sizeof(loglockfile), "%s/%s/mqtt-%s.lock",
             logdir, SERVERLOGS_LOCKDIR, ipv_inuse);
 
-#ifdef WIN32
+#ifdef _WIN32
   win32_init();
   atexit(win32_cleanup);
 

tests/server/resolve.c

@@ -102,7 +102,7 @@ int main(int argc, char *argv[])
     return 1;
   }
 
-#ifdef WIN32
+#ifdef _WIN32
   win32_init();
   atexit(win32_cleanup);
 #endif

tests/server/rtspd.c

@@ -1150,7 +1150,7 @@ int main(int argc, char *argv[])
   msnprintf(loglockfile, sizeof(loglockfile), "%s/%s/rtsp-%s.lock",
             logdir, SERVERLOGS_LOCKDIR, ipv_inuse);
 
-#ifdef WIN32
+#ifdef _WIN32
   win32_init();
   atexit(win32_cleanup);
 #endif

tests/server/sockfilt.c

@@ -152,7 +152,7 @@ enum sockmode {
   ACTIVE_DISCONNECT  /* as a client, disconnected from server */
 };
 
-#ifdef WIN32
+#ifdef _WIN32
 /*
  * read-wrapper to support reading from stdin on Windows.
  */
@@ -1461,7 +1461,7 @@ int main(int argc, char *argv[])
     }
   }
 
-#ifdef WIN32
+#ifdef _WIN32
   win32_init();
   atexit(win32_cleanup);
 

tests/server/socksd.c

@@ -1076,7 +1076,7 @@ int main(int argc, char *argv[])
     }
   }
 
-#ifdef WIN32
+#ifdef _WIN32
   win32_init();
   atexit(win32_cleanup);
 

tests/server/sws.c

@@ -2119,7 +2119,7 @@ int main(int argc, char *argv[])
             logdir, SERVERLOGS_LOCKDIR, protocol_type,
             is_proxy ? "-proxy" : "", socket_type);
 
-#ifdef WIN32
+#ifdef _WIN32
   win32_init();
   atexit(win32_cleanup);
 #endif

tests/server/tftpd.c

@@ -453,7 +453,7 @@ static ssize_t write_behind(struct testcase *test, int convert)
   if(!test->ofile) {
     char outfile[256];
     msnprintf(outfile, sizeof(outfile), "%s/upload.%ld", logdir, test->testno);
-#ifdef WIN32
+#ifdef _WIN32
     test->ofile = open(outfile, O_CREAT|O_RDWR|O_BINARY, 0777);
 #else
     test->ofile = open(outfile, O_CREAT|O_RDWR, 0777);
@@ -642,7 +642,7 @@ int main(int argc, char **argv)
   msnprintf(loglockfile, sizeof(loglockfile), "%s/%s/tftp-%s.lock",
             logdir, SERVERLOGS_LOCKDIR, ipv_inuse);
 
-#ifdef WIN32
+#ifdef _WIN32
   win32_init();
   atexit(win32_cleanup);
 #endif

tests/server/util.c

@@ -144,7 +144,7 @@ void logmsg(const char *msg, ...)
   }
 }
 
-#ifdef WIN32
+#ifdef _WIN32
 /* use instead of strerror() on generic Windows */
 static const char *win32_strerror(int err, char *buf, size_t buflen)
 {
@@ -208,7 +208,7 @@ const char *sstrerror(int err)
   static char buf[512];
   return win32_strerror(err, buf, sizeof(buf));
 }
-#endif  /* WIN32 */
+#endif  /* _WIN32 */
 
 /* set by the main code to point to where the test dir is */
 const char *path = ".";
@@ -292,7 +292,7 @@ curl_off_t our_getpid(void)
   curl_off_t pid;
 
   pid = (curl_off_t)getpid();
-#if defined(WIN32) || defined(_WIN32)
+#if defined(_WIN32) || defined(_WIN32)
   /* store pid + 65536 to avoid conflict with Cygwin/msys PIDs, see also:
    * - https://cygwin.com/git/?p=newlib-cygwin.git;a=commit; ↵
    *   h=b5e1003722cb14235c4f166be72c09acdffc62ea
@@ -378,7 +378,7 @@ void clear_advisor_read_lock(const char *filename)
 }
 
 
-#if defined(WIN32) && !defined(MSDOS)
+#if defined(_WIN32) && !defined(MSDOS)
 
 static struct timeval tvnow(void)
 {
@@ -501,11 +501,11 @@ static SIGHANDLER_T old_sigint_handler  = SIG_ERR;
 static SIGHANDLER_T old_sigterm_handler = SIG_ERR;
 #endif
 
-#if defined(SIGBREAK) && defined(WIN32)
+#if defined(SIGBREAK) && defined(_WIN32)
 static SIGHANDLER_T old_sigbreak_handler = SIG_ERR;
 #endif
 
-#ifdef WIN32
+#ifdef _WIN32
 #ifdef _WIN32_WCE
 static DWORD thread_main_id = 0;
 #else
@@ -521,7 +521,7 @@ volatile int got_exit_signal = 0;
 /* if next is set indicates the first signal handled in exit_signal_handler */
 volatile int exit_signal = 0;
 
-#ifdef WIN32
+#ifdef _WIN32
 /* event which if set indicates that the program should finish */
 HANDLE exit_event = NULL;
 #endif
@@ -538,7 +538,7 @@ static void exit_signal_handler(int signum)
   if(got_exit_signal == 0) {
     got_exit_signal = 1;
     exit_signal = signum;
-#ifdef WIN32
+#ifdef _WIN32
     if(exit_event)
       (void)SetEvent(exit_event);
 #endif
@@ -547,7 +547,7 @@ static void exit_signal_handler(int signum)
   errno = old_errno;
 }
 
-#ifdef WIN32
+#ifdef _WIN32
 /* CTRL event handler for Windows Console applications to simulate
  * SIGINT, SIGTERM and SIGBREAK on CTRL events and trigger signal handler.
  *
@@ -698,7 +698,7 @@ static SIGHANDLER_T set_signal(int signum, SIGHANDLER_T handler,
 
 void install_signal_handlers(bool keep_sigalrm)
 {
-#ifdef WIN32
+#ifdef _WIN32
 #ifdef _WIN32_WCE
   typedef HANDLE curl_win_thread_handle_t;
 #else
@@ -744,13 +744,13 @@ void install_signal_handlers(bool keep_sigalrm)
   if(old_sigterm_handler == SIG_ERR)
     logmsg("cannot install SIGTERM handler: %s", strerror(errno));
 #endif
-#if defined(SIGBREAK) && defined(WIN32)
+#if defined(SIGBREAK) && defined(_WIN32)
   /* handle SIGBREAK signal with our exit_signal_handler */
   old_sigbreak_handler = set_signal(SIGBREAK, exit_signal_handler, TRUE);
   if(old_sigbreak_handler == SIG_ERR)
     logmsg("cannot install SIGBREAK handler: %s", strerror(errno));
 #endif
-#ifdef WIN32
+#ifdef _WIN32
   if(!SetConsoleCtrlHandler(ctrl_event_handler, TRUE))
     logmsg("cannot install CTRL event handler");
 #ifdef _WIN32_WCE
@@ -792,11 +792,11 @@ void restore_signal_handlers(bool keep_sigalrm)
   if(SIG_ERR != old_sigterm_handler)
     (void) set_signal(SIGTERM, old_sigterm_handler, FALSE);
 #endif
-#if defined(SIGBREAK) && defined(WIN32)
+#if defined(SIGBREAK) && defined(_WIN32)
   if(SIG_ERR != old_sigbreak_handler)
     (void) set_signal(SIGBREAK, old_sigbreak_handler, FALSE);
 #endif
-#ifdef WIN32
+#ifdef _WIN32
   (void)SetConsoleCtrlHandler(ctrl_event_handler, FALSE);
   if(thread_main_window && thread_main_id) {
     if(PostThreadMessage(thread_main_id, WM_APP, 0, 0)) {
@@ -846,7 +846,7 @@ int bind_unix_socket(curl_socket_t sock, const char *unix_socket,
         return rc;
       }
       /* socket server is not alive, now check if it was actually a socket. */
-#ifdef WIN32
+#ifdef _WIN32
       /* Windows does not have lstat function. */
       rc = curlx_win32_stat(unix_socket, &statbuf);
 #else

tests/server/util.h

@@ -41,7 +41,7 @@ extern const char *serverlogfile;
 
 extern const char *cmdfile;
 
-#ifdef WIN32
+#ifdef _WIN32
 #include <process.h>
 #include <fcntl.h>
 
@@ -54,10 +54,10 @@ void win32_perror(const char *msg);
 void win32_init(void);
 void win32_cleanup(void);
 const char *sstrerror(int err);
-#else   /* WIN32 */
+#else   /* _WIN32 */
 
 #define sstrerror(e) strerror(e)
-#endif  /* WIN32 */
+#endif  /* _WIN32 */
 
 /* fopens the test case file */
 FILE *test2fopen(long testno, const char *logdir);
@@ -75,7 +75,7 @@ extern volatile int got_exit_signal;
 /* global variable which if set indicates the first signal handled */
 extern volatile int exit_signal;
 
-#ifdef WIN32
+#ifdef _WIN32
 /* global event which if set indicates that the program should finish */
 extern HANDLE exit_event;
 #endif