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

fusl/src/string/strerror_r.c

Index: fusl/src/string/strerror_r.c
diff --git a/fusl/src/string/strerror_r.c b/fusl/src/string/strerror_r.c
new file mode 100644
index 0000000000000000000000000000000000000000..da26b4fe9875a13839ce0b105fade0c13fc12712
--- /dev/null
+++ b/fusl/src/string/strerror_r.c
@@ -0,0 +1,20 @@
+#include <string.h>
+#include <errno.h>
+#include "libc.h"
+
+int strerror_r(int err, char *buf, size_t buflen)
+{
+	char *msg = strerror(err);
+	size_t l = strlen(msg);
+	if (l >= buflen) {
+		if (buflen) {
+			memcpy(buf, msg, buflen-1);
+			buf[buflen-1] = 0;
+		}
+		return ERANGE;
+	}
+	memcpy(buf, msg, l+1);
+	return 0;
+}
+
+weak_alias(strerror_r, __xpg_strerror_r);