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

fusl/src/stdio/__fopen_rb_ca.c

Index: fusl/src/stdio/__fopen_rb_ca.c
diff --git a/fusl/src/stdio/__fopen_rb_ca.c b/fusl/src/stdio/__fopen_rb_ca.c
new file mode 100644
index 0000000000000000000000000000000000000000..183a5d553895537199ca452bc593ea69ea77e146
--- /dev/null
+++ b/fusl/src/stdio/__fopen_rb_ca.c
@@ -0,0 +1,22 @@
+#include "stdio_impl.h"
+#include <fcntl.h>
+#include <string.h>
+
+FILE *__fopen_rb_ca(const char *filename, FILE *f, unsigned char *buf, size_t len)
+{
+	memset(f, 0, sizeof *f);
+
+	f->fd = sys_open(filename, O_RDONLY|O_CLOEXEC);
+	if (f->fd < 0) return 0;
+	__syscall(SYS_fcntl, f->fd, F_SETFD, FD_CLOEXEC);
+
+	f->flags = F_NOWR | F_PERM;
+	f->buf = buf + UNGET;
+	f->buf_size = len - UNGET;
+	f->read = __stdio_read;
+	f->seek = __stdio_seek;
+	f->close = __stdio_close;
+	f->lock = -1;
+
+	return f;
+}