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

fusl/src/legacy/utmpx.c

+#include <utmpx.h>
+#include <stddef.h>
+#include "libc.h"
+
+void endutxent(void)
+{
+}
+
+void setutxent(void)
+{
+}
+
+struct utmpx *getutxent(void)
+{
+        return NULL;
+}
+
+struct utmpx *getutxid(const struct utmpx *ut)
+{
+        return NULL;
+}
+
+struct utmpx *getutxline(const struct utmpx *ut)
+{
+        return NULL;
+}
+
+struct utmpx *pututxline(const struct utmpx *ut)
+{
+        return NULL;
+}
+
+void updwtmpx(const char *f, const struct utmpx *u)
+{
+}
+
+weak_alias(endutxent, endutent);
+weak_alias(setutxent, setutent);
+weak_alias(getutxent, getutent);
+weak_alias(getutxid, getutid);
+weak_alias(getutxline, getutline);
+weak_alias(pututxline, pututline);
+weak_alias(updwtmpx, updwtmp);