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

fusl/src/fcntl/posix_fadvise.c

Index: fusl/src/fcntl/posix_fadvise.c
diff --git a/fusl/src/fcntl/posix_fadvise.c b/fusl/src/fcntl/posix_fadvise.c
new file mode 100644
index 0000000000000000000000000000000000000000..d5360e0fc4279d2486541856d131160e9e46644d
--- /dev/null
+++ b/fusl/src/fcntl/posix_fadvise.c
@@ -0,0 +1,11 @@
+#include <fcntl.h>
+#include "syscall.h"
+#include "libc.h"
+
+int posix_fadvise(int fd, off_t base, off_t len, int advice)
+{
+	return -(__syscall)(SYS_fadvise, fd, __SYSCALL_LL_O(base),
+		__SYSCALL_LL_E(len), advice);
+}
+
+LFS64(posix_fadvise);