enable windows colour console support

and thus enable support for:
 - colour console logging.
 - colour help text.
 - colour highlighting of errors and warnings when parsing commandline
   arguments on windows.

according to [1] microsoft provide `isatty()` support under the name
`_isatty()` in `io.h` due to it being non-standard.

i was originally going to attempt to duplicate the use of the
`GetConsoleMode()` function as done in the rust `atty` crate, but the
existence of `_isatty()` is much more simple. it's left me confused over
why the rust crate uses `GetConsoleMode()` instead. i have not turned up
any info so far about when `_isatty()` was introduced on windows, so maybe
its too new? maybe it doesn't support special environments like cygwin? i
have noted that it was already in use by `src/text/unicode.c`.

[1]: https://docs.microsoft.com/en-us/cpp/c-runtime-library/reference/isatty?view=msvc-170

include/vlc_fixups.h

@@ -675,6 +675,11 @@ int clock_nanosleep(clockid_t clock_id, int flags,
 # endif
 #endif
 
+#ifdef _WIN32
+# include <io.h>
+# define isatty(x) _isatty(x)
+#endif
+
 #ifdef __cplusplus
 } /* extern "C" */
 #endif

modules/logger/console.c

@@ -154,7 +154,7 @@ static const struct vlc_logger_operations *Open(vlc_object_t *obj,
 
     *sysp = verbosities + verbosity;
 
-#if defined (HAVE_ISATTY) && !defined (_WIN32)
+#if defined (HAVE_ISATTY)
     if (isatty(STDERR_FILENO) && var_InheritBool(obj, "color"))
         return &color_ops;
 #endif

src/config/cmdline.c

@@ -182,10 +182,7 @@ int config_LoadCmdLine( vlc_object_t *p_this, int i_argc,
     psz_shortopts[i_shortopts] = '\0';
 
     int ret = -1;
-    bool color = false;
-#ifndef _WIN32
-    color = (isatty(STDERR_FILENO));
-#endif
+    bool color = isatty(STDERR_FILENO);
 
     /*
      * Parse the command line options

src/config/help.c

@@ -584,10 +584,8 @@ static void Usage (vlc_object_t *p_this, char const *psz_search)
     }
 
     bool color = false;
-#ifndef _WIN32
     if (isatty(STDOUT_FILENO))
         color = var_InheritBool(p_this, "color");
-#endif
 
     const bool desc = var_InheritBool(p_this, "help-verbose");
 
@@ -646,12 +644,8 @@ static void ListModules (vlc_object_t *p_this, bool b_verbose)
     bool color = false;
 
     ShowConsole();
-#ifndef _WIN32
     if (isatty(STDOUT_FILENO))
         color = var_InheritBool(p_this, "color");
-#else
-    (void) p_this;
-#endif
 
     /* List all modules */
     size_t count;

src/text/unicode.c

@@ -39,9 +39,6 @@
 #include <stdarg.h>
 #include <stdlib.h>
 #include <sys/types.h>
-#if defined(_WIN32)
-#  include <io.h>
-#endif
 #include <errno.h>
 #include <wctype.h>
 
@@ -65,7 +62,7 @@ int utf8_vfprintf( FILE *stream, const char *fmt, va_list ap )
      * which is different from the usual ANSI code page. Or maybe not, if the
      * user called "chcp". Anyway, we prefer Unicode. */
     int fd = _fileno (stream);
-    if (likely(fd != -1) && _isatty (fd))
+    if (likely(fd != -1) && isatty (fd))
     {
         wchar_t *wide = ToWide (str);
         if (likely(wide != NULL))