Reserve space in mbstate to allow for proper wchar support

Bug: 14382788
Change-Id: If023ac9bb65f95135cae7ebe89147e3985a69a96
diff --git a/libc/include/limits.h b/libc/include/limits.h
index a70021a..dc45902 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -112,7 +112,7 @@
 
 #define SSIZE_MAX LONG_MAX
 
-#define MB_LEN_MAX 1 /* No multibyte characters. */
+#define MB_LEN_MAX 6
 
 /* New code should use sysconf(_SC_PAGE_SIZE) instead. */
 #ifndef PAGE_SIZE