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

fusl/src/misc/getsubopt.c

Index: fusl/src/misc/getsubopt.c
diff --git a/fusl/src/misc/getsubopt.c b/fusl/src/misc/getsubopt.c
new file mode 100644
index 0000000000000000000000000000000000000000..53ee9573f2fce5430b13424dfabb77f9253d0b97
--- /dev/null
+++ b/fusl/src/misc/getsubopt.c
@@ -0,0 +1,23 @@
+#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;
+}