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

fusl/include/sys/eventfd.h

Index: fusl/include/sys/eventfd.h
diff --git a/fusl/include/sys/eventfd.h b/fusl/include/sys/eventfd.h
new file mode 100644
index 0000000000000000000000000000000000000000..dc5c88f041fb5084a4d1ebea2d8e540292ea4a88
--- /dev/null
+++ b/fusl/include/sys/eventfd.h
@@ -0,0 +1,26 @@
+#ifndef _SYS_EVENTFD_H
+#define _SYS_EVENTFD_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdint.h>
+#include <fcntl.h>
+
+typedef uint64_t eventfd_t;
+
+#define EFD_SEMAPHORE 1
+#define EFD_CLOEXEC O_CLOEXEC
+#define EFD_NONBLOCK O_NONBLOCK
+
+int eventfd(unsigned int, int);
+int eventfd_read(int, eventfd_t *);
+int eventfd_write(int, eventfd_t);
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* sys/eventfd.h */