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

fusl/arch/arm/src/__aeabi_memset.c

Index: fusl/arch/arm/src/__aeabi_memset.c
diff --git a/fusl/arch/arm/src/__aeabi_memset.c b/fusl/arch/arm/src/__aeabi_memset.c
new file mode 100644
index 0000000000000000000000000000000000000000..89299757f22219ea9ec454a9933721dae6378b89
--- /dev/null
+++ b/fusl/arch/arm/src/__aeabi_memset.c
@@ -0,0 +1,9 @@
+#include <string.h>
+#include "libc.h"
+
+void __aeabi_memset(void *dest, size_t n, int c)
+{
+	memset(dest, c, n);
+}
+weak_alias(__aeabi_memset, __aeabi_memset4);
+weak_alias(__aeabi_memset, __aeabi_memset8);