Make multibyte result constants public.

The magic numbers that C defines are obnoxious. We had partial
definitions for these internally. Add the missing one and move them to
a public header for anyone else that may want to use them.

Bug: None
Test: None
Change-Id: Ia6b8cff4310bcccb23078c52216528db668ac966
diff --git a/libc/bionic/wchar.cpp b/libc/bionic/wchar.cpp
index bb97b3e..b8c4432 100644
--- a/libc/bionic/wchar.cpp
+++ b/libc/bionic/wchar.cpp
@@ -27,10 +27,10 @@
  */
 
 #include <errno.h>
-#include <sys/param.h>
 #include <string.h>
-#include <wchar.h>
+#include <sys/param.h>
 #include <uchar.h>
+#include <wchar.h>
 
 #include "private/bionic_mbstate.h"
 
@@ -88,10 +88,10 @@
         r = 1;
       } else {
         r = mbrtowc(nullptr, *src + i, nmc - i, state);
-        if (r == __MB_ERR_ILLEGAL_SEQUENCE) {
+        if (r == BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE) {
           return mbstate_reset_and_return_illegal(EILSEQ, state);
         }
-        if (r == __MB_ERR_INCOMPLETE_SEQUENCE) {
+        if (r == BIONIC_MULTIBYTE_RESULT_INCOMPLETE_SEQUENCE) {
           return mbstate_reset_and_return_illegal(EILSEQ, state);
         }
         if (r == 0) {
@@ -114,11 +114,11 @@
       }
     } else {
       r = mbrtowc(dst + o, *src + i, nmc - i, state);
-      if (r == __MB_ERR_ILLEGAL_SEQUENCE) {
+      if (r == BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE) {
         *src += i;
         return mbstate_reset_and_return_illegal(EILSEQ, state);
       }
-      if (r == __MB_ERR_INCOMPLETE_SEQUENCE) {
+      if (r == BIONIC_MULTIBYTE_RESULT_INCOMPLETE_SEQUENCE) {
         *src += nmc;
         return mbstate_reset_and_return_illegal(EILSEQ, state);
       }
@@ -166,7 +166,7 @@
         r = 1;
       } else {
         r = wcrtomb(buf, wc, state);
-        if (r == __MB_ERR_ILLEGAL_SEQUENCE) {
+        if (r == BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE) {
           return r;
         }
       }
@@ -187,14 +187,14 @@
     } else if (len - o >= sizeof(buf)) {
       // Enough space to translate in-place.
       r = wcrtomb(dst + o, wc, state);
-      if (r == __MB_ERR_ILLEGAL_SEQUENCE) {
+      if (r == BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE) {
         *src += i;
         return r;
       }
     } else {
       // May not be enough space; use temp buffer.
       r = wcrtomb(buf, wc, state);
-      if (r == __MB_ERR_ILLEGAL_SEQUENCE) {
+      if (r == BIONIC_MULTIBYTE_RESULT_ILLEGAL_SEQUENCE) {
         *src += i;
         return r;
       }