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

fusl/src/linux/eventfd.c

+#include <sys/eventfd.h>
+#include <unistd.h>
+#include <errno.h>
+#include "syscall.h"
+
+int eventfd(unsigned int count, int flags)
+{
+        int r = __syscall(SYS_eventfd2, count, flags);
+#ifdef SYS_eventfd
+        if (r==-ENOSYS && !flags) r = __syscall(SYS_eventfd, count);
+#endif
+        return __syscall_ret(r);
+}
+
+int eventfd_read(int fd, eventfd_t *value)
+{
+        return (sizeof(*value) == read(fd, value, sizeof(*value))) ? 0 : -1;
+}
+
+int eventfd_write(int fd, eventfd_t value)
+{
+        return (sizeof(value) == write(fd, &value, sizeof(value))) ? 0 : -1;
+}