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

fusl/src/unistd/getlogin_r.c

Index: fusl/src/unistd/getlogin_r.c
diff --git a/fusl/src/unistd/getlogin_r.c b/fusl/src/unistd/getlogin_r.c
new file mode 100644
index 0000000000000000000000000000000000000000..53866c6dce4077d8a53ba118a6460c2f2e6f55ee
--- /dev/null
+++ b/fusl/src/unistd/getlogin_r.c
@@ -0,0 +1,12 @@
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+int getlogin_r(char *name, size_t size)
+{
+	char *logname = getlogin();
+	if (!logname) return ENXIO; /* or...? */
+	if (strlen(logname) >= size) return ERANGE;
+	strcpy(name, logname);
+	return 0;
+}