mbstate_t is a struct that is required. However, it is not defined by mes libc.
This implementation was taken from glibc 2.32. 

--- lib/quotearg.c	2002-11-23 07:08:10.000000000 +0000
+++ lib/quotearg.c	2021-01-17 19:41:59.461095532 +0000
@@ -21,6 +21,7 @@
 # include <config.h>
 #endif
 
+#include "mbstate_t.h"
 #include "quotearg.h"
 
 #include "xalloc.h"
--- lib/mbstate_t.h	1970-01-01 01:00:00.000000000 +0100
+++ lib/mbstate_t.h	2021-01-17 19:42:21.341658668 +0000
@@ -0,0 +1,23 @@
+#ifndef ____mbstate_t_defined
+#define ____mbstate_t_defined 1
+
+/* Integral type unchanged by default argument promotions that can
+   hold any value corresponding to members of the extended character
+   set, as well as at least one value that does not correspond to any
+   member of the extended character set.  */
+#ifndef __WINT_TYPE__
+# define __WINT_TYPE__ unsigned int
+#endif
+
+/* Conversion state information.  */
+typedef struct
+{
+  int __count;
+  union
+  {
+    __WINT_TYPE__ __wch;
+    char __wchb[4];
+  } __value;		/* Value so far.  */
+} mbstate_t;
+
+#endif