update from texinfo
mbsstr, quotearg, xstrtol: pacify IRIX 6.5 cc

These were found when building the latest grep snapshot on IRIX 6.5.
* lib/mbsstr.c (knuth_morris_pratt_multibyte): Break "a=b=c;" into
"b=c; a=b;", since IRIX 6.5 cc complains about the former if b is
never used later.
* lib/quotearg.c (quoting_options_from_style):
* lib/xstrtol.c (__xstrtol):
Use enum instead of 0, to pacify IRIX 6.5 cc.
getlogin-tests: avoid false failure under sudo/ssh etc.

* modules/getlogin-tests (configure.ac): Check for ttyname().
* tests/test-getlogin.c (main): Don't depend on environment variables
to correlate with getlogin(), since sudo and ssh etc. can tamper
with the LOGNAME and USER env vars.  Instead lookup the name from
the uid associated with the stdin tty.
autoupdate