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

fusl/src/locale/newlocale.c

+#include <stdlib.h>
+#include <string.h>
+#include "locale_impl.h"
+#include "libc.h"
+
+int __loc_is_allocated(locale_t loc)
+{
+        return loc && loc != C_LOCALE && loc != UTF8_LOCALE;
+}
+
+locale_t __newlocale(int mask, const char *name, locale_t loc)
+{
+        int i, j;
+        struct __locale_struct tmp;
+        const struct __locale_map *lm;
+
+        /* For locales with allocated storage, modify in-place. */
+        if (__loc_is_allocated(loc)) {
+                for (i=0; i<LC_ALL; i++)
+                        if (mask & (1<<i))
+                                loc->cat[i] = __get_locale(i, name);
+                return loc;
+        }
+
+        /* Otherwise, build a temporary locale object, which will only
+         * be instantiated in allocated storage if it does not match
+         * one of the built-in static locales. This makes the common
+         * usage case for newlocale, getting a C locale with predictable
+         * behavior, very fast, and more importantly, fail-safe. */
+        for (j=i=0; i<LC_ALL; i++) {
+                if (loc && !(mask & (1<<i)))
+                        lm = loc->cat[i];
+                else
+                        lm = __get_locale(i, mask & (1<<i) ? name : "");
+                if (lm) j++;
+                tmp.cat[i] = lm;
+        }
+
+        if (!j)
+                return C_LOCALE;
+        if (j==1 && tmp.cat[LC_CTYPE]==&__c_dot_utf8)
+                return UTF8_LOCALE;
+
+        if ((loc = malloc(sizeof *loc))) *loc = tmp;
+
+        return loc;
+}
+
+weak_alias(__newlocale, newlocale);