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

fusl/src/misc/getsubopt.c

+#include <stdlib.h>
+#include <string.h>
+
+int getsubopt(char **opt, char *const *keys, char **val)
+{
+        char *s = *opt;
+        int i;
+
+        *val = NULL;
+        *opt = strchr(s, ',');
+        if (*opt) *(*opt)++ = 0;
+        else *opt = s + strlen(s);
+
+        for (i=0; keys[i]; i++) {
+                size_t l = strlen(keys[i]);
+                if (strncmp(keys[i], s, l)) continue;
+                if (s[l] == '=')
+                        *val = s + l + 1;
+                else if (s[l]) continue;
+                return i;
+        }
+        return -1;
+}