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

fusl/src/stdio/fopen.c

Index: fusl/src/stdio/fopen.c
diff --git a/fusl/src/stdio/fopen.c b/fusl/src/stdio/fopen.c
new file mode 100644
index 0000000000000000000000000000000000000000..252f08241b3a313c057b3c6d8fc6baa1e8278c43
--- /dev/null
+++ b/fusl/src/stdio/fopen.c
@@ -0,0 +1,33 @@
+#include "stdio_impl.h"
+#include <fcntl.h>
+#include <string.h>
+#include <errno.h>
+
+FILE *fopen(const char *restrict filename, const char *restrict mode)
+{
+	FILE *f;
+	int fd;
+	int flags;
+
+	/* Check for valid initial mode character */
+	if (!strchr("rwa", *mode)) {
+		errno = EINVAL;
+		return 0;
+	}
+
+	/* Compute the flags to pass to open() */
+	flags = __fmodeflags(mode);
+
+	fd = sys_open(filename, flags, 0666);
+	if (fd < 0) return 0;
+	if (flags & O_CLOEXEC)
+		__syscall(SYS_fcntl, fd, F_SETFD, FD_CLOEXEC);
+
+	f = __fdopen(fd, mode);
+	if (f) return f;
+
+	__syscall(SYS_close, fd);
+	return 0;
+}
+
+LFS64(fopen);