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

fusl/src/fcntl/posix_fallocate.c

Index: fusl/src/fcntl/posix_fallocate.c
diff --git a/fusl/src/fcntl/posix_fallocate.c b/fusl/src/fcntl/posix_fallocate.c
new file mode 100644
index 0000000000000000000000000000000000000000..91d8063ca45815757bdb63478e91f85b1a4f8990
--- /dev/null
+++ b/fusl/src/fcntl/posix_fallocate.c
@@ -0,0 +1,11 @@
+#include <fcntl.h>
+#include "syscall.h"
+#include "libc.h"
+
+int posix_fallocate(int fd, off_t base, off_t len)
+{
+	return -__syscall(SYS_fallocate, fd, 0, __SYSCALL_LL_E(base),
+		__SYSCALL_LL_E(len));
+}
+
+LFS64(posix_fallocate);