[PATCH] handle multibyte stores larger than char in strlen (PR 91183, 86888)

[Martin Sebor]

> Committed in r273783 after retesting and including a test for
> the warning that I had left out of the patch I posted here.
> 
> Martin
> 
> PS I suspect some of the tests I added might need tweaking on
> big-endian systems.  I'll deal with them tomorrow.

And maybe also strictly aligned targets.  A sparc-solaris2.11 cross
shows these failures.  It looks like it doesn't like something about
some of the 64 bit stores in the tests.

FAIL: gcc.dg/strlenopt-70.c scan-tree-dump-times optimized "strlen" 0
FAIL: gcc.dg/strlenopt-70.c scan-tree-dump-times optimized 
"_not_eliminated_" 0
FAIL: gcc.dg/strlenopt-71.c (test for excess errors)
FAIL: gcc.dg/strlenopt-72.c scan-tree-dump-times optimized "strlen" 0
FAIL: gcc.dg/strlenopt-72.c scan-tree-dump-times optimized 
"_not_eliminated_" 0