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

fusl/src/stdio/fputwc.c

+#include "stdio_impl.h"
+#include "locale_impl.h"
+#include <wchar.h>
+#include <limits.h>
+#include <ctype.h>
+
+wint_t __fputwc_unlocked(wchar_t c, FILE *f)
+{
+        char mbc[MB_LEN_MAX];
+        int l;
+        locale_t *ploc = &CURRENT_LOCALE, loc = *ploc;
+
+        if (f->mode <= 0) fwide(f, 1);
+        *ploc = f->locale;
+
+        if (isascii(c)) {
+                c = putc_unlocked(c, f);
+        } else if (f->wpos + MB_LEN_MAX < f->wend) {
+                l = wctomb((void *)f->wpos, c);
+                if (l < 0) c = WEOF;
+                else f->wpos += l;
+        } else {
+                l = wctomb(mbc, c);
+                if (l < 0 || __fwritex((void *)mbc, l, f) < l) c = WEOF;
+        }
+        if (c==WEOF) f->flags |= F_ERR;
+        *ploc = loc;
+        return c;
+}
+
+wint_t fputwc(wchar_t c, FILE *f)
+{
+        FLOCK(f);
+        c = __fputwc_unlocked(c, f);
+        FUNLOCK(f);
+        return c;
+}
+
+weak_alias(__fputwc_unlocked, fputwc_unlocked);
+weak_alias(__fputwc_unlocked, putwc_unlocked);