Fix the printf family for non-ASCII.

The bug here turned out to be that we hadn't increased the constant
corresponding to the maximum number of bytes in a character to match
our new implementation, so any character requiring more than a byte
in UTF-8 would break our printf family.

Bug: 15439554
Change-Id: I693e5e6eb11c640b5886e848502908ec5fff53b1
diff --git a/libc/include/limits.h b/libc/include/limits.h
index dc45902..fb09657 100644
--- a/libc/include/limits.h
+++ b/libc/include/limits.h
@@ -112,7 +112,7 @@
 
 #define SSIZE_MAX LONG_MAX
 
-#define MB_LEN_MAX 6
+#define MB_LEN_MAX 4
 
 /* New code should use sysconf(_SC_PAGE_SIZE) instead. */
 #ifndef PAGE_SIZE