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

fusl/src/mman/posix_madvise.c

Index: fusl/src/mman/posix_madvise.c
diff --git a/fusl/src/mman/posix_madvise.c b/fusl/src/mman/posix_madvise.c
new file mode 100644
index 0000000000000000000000000000000000000000..e5e5acb84aba85765096b00058c3804aa8a2402a
--- /dev/null
+++ b/fusl/src/mman/posix_madvise.c
@@ -0,0 +1,9 @@
+#define _GNU_SOURCE
+#include <sys/mman.h>
+#include "syscall.h"
+
+int posix_madvise(void *addr, size_t len, int advice)
+{
+	if (advice == MADV_DONTNEED) return 0;
+	return -__syscall(SYS_madvise, addr, len, advice);
+}