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

fusl/src/internal/procfdname.c

Index: fusl/src/internal/procfdname.c
diff --git a/fusl/src/internal/procfdname.c b/fusl/src/internal/procfdname.c
new file mode 100644
index 0000000000000000000000000000000000000000..697e0bdc2e1f6a2ae212f70a5915b99cc35d1dfd
--- /dev/null
+++ b/fusl/src/internal/procfdname.c
@@ -0,0 +1,13 @@
+void __procfdname(char *buf, unsigned fd)
+{
+	unsigned i, j;
+	for (i=0; (buf[i] = "/proc/self/fd/"[i]); i++);
+	if (!fd) {
+		buf[i] = '0';
+		buf[i+1] = 0;
+		return;
+	}
+	for (j=fd; j; j/=10, i++);
+	buf[i] = 0;
+	for (; fd; fd/=10) buf[--i] = '0' + fd%10;
+}