Add a "fork" of musl as //fusl.

fusl/src/time/wcsftime.c

+#include <wchar.h>
+#include <time.h>
+#include <locale.h>
+#include "locale_impl.h"
+#include "libc.h"
+
+const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *tm, locale_t loc);
+
+size_t __wcsftime_l(wchar_t *restrict s, size_t n, const wchar_t *restrict f, const struct tm *restrict tm, locale_t loc)
+{
+        size_t l, k;
+        char buf[100];
+        wchar_t wbuf[100];
+        wchar_t *p;
+        const char *t_mb;
+        const wchar_t *t;
+        int plus;
+        unsigned long width;
+        for (l=0; l<n; f++) {
+                if (!*f) {
+                        s[l] = 0;
+                        return l;
+                }
+                if (*f != '%') {
+                        s[l++] = *f;
+                        continue;
+                }
+                f++;
+                if ((plus = (*f == '+'))) f++;
+                width = wcstoul(f, &p, 10);
+                if (*p == 'C' || *p == 'F' || *p == 'G' || *p == 'Y') {
+                        if (!width && p!=f) width = 1;
+                } else {
+                        width = 0;
+                }
+                f = p;
+                if (*f == 'E' || *f == 'O') f++;
+                t_mb = __strftime_fmt_1(&buf, &k, *f, tm, loc);
+                if (!t_mb) break;
+                k = mbstowcs(wbuf, t_mb, sizeof wbuf / sizeof *wbuf);
+                if (k == (size_t)-1) return 0;
+                t = wbuf;
+                if (width) {
+                        for (; *t=='+' || *t=='-' || (*t=='0'&&t[1]); t++, k--);
+                        width--;
+                        if (plus && tm->tm_year >= 10000-1900)
+                                s[l++] = '+';
+                        else if (tm->tm_year < -1900)
+                                s[l++] = '-';
+                        else
+                                width++;
+                        for (; width > k && l < n; width--)
+                                s[l++] = '0';
+                }
+                if (k >= n-l) k = n-l;
+                wmemcpy(s+l, t, k);
+                l += k;
+        }
+        if (n) {
+                if (l==n) l=n-1;
+                s[l] = 0;
+        }
+        return 0;
+}
+
+size_t wcsftime(wchar_t *restrict wcs, size_t n, const wchar_t *restrict f, const struct tm *restrict tm)
+{
+        return __wcsftime_l(wcs, n, f, tm, CURRENT_LOCALE);
+}
+
+weak_alias(__wcsftime_l, wcsftime_l);