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

fusl/src/linux/sync_file_range.c

Index: fusl/src/linux/sync_file_range.c
diff --git a/fusl/src/linux/sync_file_range.c b/fusl/src/linux/sync_file_range.c
new file mode 100644
index 0000000000000000000000000000000000000000..6859abc05dabde2825af4a392b2b0e0d255f2a4e
--- /dev/null
+++ b/fusl/src/linux/sync_file_range.c
@@ -0,0 +1,17 @@
+#define _GNU_SOURCE
+#include <fcntl.h>
+#include <errno.h>
+#include "syscall.h"
+
+int sync_file_range(int fd, off_t pos, off_t len, unsigned flags)
+{
+#if defined(SYS_sync_file_range2)
+	return syscall(SYS_sync_file_range2, fd, flags,
+		__SYSCALL_LL_E(pos), __SYSCALL_LL_E(len));
+#elif defined(SYS_sync_file_range)
+	return syscall(SYS_sync_file_range, fd,
+		__SYSCALL_LL_O(pos), __SYSCALL_LL_E(len), flags);
+#else
+	return __syscall_ret(-ENOSYS);
+#endif
+}