strcoll: Remove incorrect STRDIFF-based optimization (Bug 18589).

The optimization introduced in commit
f13c2a8dff2329c6692a80176262ceaaf8a6f74e, causes regressions in
sorting for languages that have digraphs that change sort order, like
cs_CZ which sorts ch between h and i.

My analysis shows the fast-forwarding optimization in STRCOLL advances
through a digraph while possibly stopping in the middle which results
in a subsequent skipping of the digraph and incorrect sorting. The
optimization is incorrect as implemented and because of that I'm
removing it for 2.23, and I will also commit this fix for 2.22 where
it was originally introduced.

This patch reverts the optimization, introduces a new bug-strcoll2.c
regression test that tests both cs_CZ.UTF-8 and da_DK.ISO-8859-1 and
ensures they sort one digraph each correctly. The optimization can't be
applied without regressing this test.

Checked on x86_64, bug-strcoll2.c fails without this patch and passes
after. This will also get a fix on 2.22 which has the same bug.

1 files changed, 0 insertions, 1 deletions

diff --git a/wcsmbs/wcscoll_l.c b/wcsmbs/wcscoll_l.c
index 6d9384ad64..87f240d281 100644
--- a/wcsmbs/wcscoll_l.c
+++ b/wcsmbs/wcscoll_l.c
@@ -23,7 +23,6 @@
 #define STRING_TYPE wchar_t
 #define USTRING_TYPE wint_t
 #define STRCOLL __wcscoll_l
-#define STRDIFF __wcsdiff
 #define STRCMP __wcscmp
 #define WEIGHT_H "../locale/weightwc.h"
 #define SUFFIX	WC