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

fusl/src/prng/rand_r.c

Index: fusl/src/prng/rand_r.c
diff --git a/fusl/src/prng/rand_r.c b/fusl/src/prng/rand_r.c
new file mode 100644
index 0000000000000000000000000000000000000000..638614c867911a133d4a3f054c7150e28d5a4425
--- /dev/null
+++ b/fusl/src/prng/rand_r.c
@@ -0,0 +1,15 @@
+#include <stdlib.h>
+
+static unsigned temper(unsigned x)
+{
+	x ^= x>>11;
+	x ^= x<<7 & 0x9D2C5680;
+	x ^= x<<15 & 0xEFC60000;
+	x ^= x>>18;
+	return x;
+}
+
+int rand_r(unsigned *seed)
+{
+	return temper(*seed = *seed * 1103515245 + 12345)/2;
+}