Cygwin: glob: perform correct utf-32 -> multibyte conversion

g_Ctoc, converting the UTF-32 filenames to multibyte, still
used UTF-16 to  multibyte conversion.  Introduce a wirtomb
helper and fix that.

Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/glob.cc

@@ -1024,7 +1024,7 @@ g_Ctoc(const Char *str, char *buf, size_t len)
 
 	memset(&mbs, 0, sizeof(mbs));
 	while (len >= (size_t) MB_CUR_MAX) {
-		clen = wcrtomb(buf, *str, &mbs);
+		clen = wirtomb(buf, *str, &mbs);
 		if (clen == (size_t)-1)
 			return (1);
 		if (*str == L'\0')

winsup/cygwin/local_includes/wchar.h

@@ -44,6 +44,10 @@ extern wctomb_f __utf8_wctomb;
    for surrogate pairs, plus a wchar_t NUL. */
 void wcintowcs (wchar_t *, wint_t *, size_t);
 
+/* replacement function for wcrtomb, converting a UTF-32 char to a
+   multibyte string. */
+size_t wirtomb (char *, wint_t, mbstate_t *);
+
 /* replacement function for mbrtowc, returning a wint_t representing
    a UTF-32 value. Defined in strfuncs.cc */
 extern size_t mbrtowi (wint_t *, const char *, size_t, mbstate_t *);

winsup/cygwin/strfuncs.cc

@@ -129,6 +129,25 @@ wcintowcs (wchar_t *dest, wint_t *src, size_t len)
   *dest = '\0';
 }
 
+/* replacement function for wcrtomb, converting a UTF-32 char to a
+   multibyte string. */
+extern "C" size_t
+wirtomb (char *s, wint_t wi, mbstate_t *ps)
+{
+    wchar_t wc[3] = { (wchar_t) wi, '\0', '\0' };
+    const wchar_t *wcp = wc;
+    size_t nwc = 1;
+
+    if (wi >= 0x10000)
+      {
+	wi -= 0x10000;
+	wc[0] = (wi >> 10) + 0xd800;
+	wc[1] = (wi & 0x3ff) + 0xdc00;
+	nwc = 2;
+      }
+    return wcsnrtombs (s, &wcp, nwc, SIZE_MAX, ps);
+}
+
 /* replacement function for mbrtowc, returning a wint_t representing
    a UTF-32 value. */
 extern "C" size_t