Finish making zsh Bourne-compatible

[Noah Misch]

This patch against Autoconf CVS HEAD adds to the series of commands m4sh
programs use to place zsh in a Bourne-compatible mode.  When placed in
sh-compatible mode via ``emulate sh'' or invocation under the name ``sh'', zsh
enables its GLOB_SUBST option, which causes it to make very strange choices
about when to perform quote removal of backslashes.  Consider this:

$ cat >quote.sh
a='\\\\\\\\'
b="`echo '\\\\\\\\'`"
c=`echo '\\\\\\\\'`
echo "$a" $a "$b" $b "$c" $c
^D

$ bash quote.sh
\\\\\\\\ \\\\\\\\ \\\\ \\\\ \\\\ \\\\

$ zsh quote.sh quote.sh
\\\\ \\\\ \ \ \ \

$ sh quote.sh # sh is zsh; GLOB_SUBST set implicitly
\\\\\\\\ \\\\ \\\\ \\ \\ \

$ sh -o NO_GLOB_SUBST quote.sh # sh is zsh
\\\\\\\\ \\\\\\\\ \\\\ \\\\ \\\\ \\\\

$ uname -s -r -p -m
SunOS 5.7 sun4u sparc
$ sh quote.sh
\\\\ \\\\ \ \ \ \

Autoconf has been using zsh in the third style on systems with /bin/sh as zsh
(Mac OS X 10.0, 10.1), and this patch effectively makes it use the fourth style.

I observed this behavior while debugging a failure in the libtool test suite on
Mac OS X 10.1.  This patch fixes many libtool tests on that platform.  Though
libtool was already setting this shell option correctly in some places, certain
declarations (e.g. lt_cv_sys_global_symbol_to_c_name_address) in libtool.m4 were
initialized in the configure script before the first such setopt.  Since this
makes all configure.in scripts more portable, I thought it belonged in m4sh, at
the top of every configure script, with the other zsh compatibility settings.

I welcome your feedback.  I tested this change on a Fedora Core 1 system and all
Autoconf tests continue to pass.  I really cannot run the Autoconf test suite on
Mac OS X with zsh, though.  It could take _weeks_.  I will post a demonstration
of the improved libtool test suite behavior with a forthcoming patch to
address@hidden, though.

On a related note, I collected enough information on quote removal behaviors in
various shells to add a section documenting them to the the Portable Shell
section of the Autoconf manual.  Would that interest folks?

2004-06-23  Noah Misch  <address@hidden>

        * lib/m4sugar/m4sh.m4 (_AS_BOURNE_COMPATIBLE): If the shell is
        zsh, disable GLOB_SUBST to avoid backslash handling problems.

Index: lib/m4sugar/m4sh.m4
===================================================================
RCS file: /cvsroot/autoconf/autoconf/lib/m4sugar/m4sh.m4,v
retrieving revision 1.115
diff -u -r1.115 m4sh.m4
--- lib/m4sugar/m4sh.m4 3 May 2004 03:49:22 -0000       1.115
+++ lib/m4sugar/m4sh.m4 23 Jun 2004 22:47:29 -0000
@@ -161,6 +161,7 @@
   [#] Zsh 3.x and 4.x performs word splitting on ${1+"address@hidden"}, which
   # is contrary to our usage.  Disable this feature.
   alias -g '${1+"address@hidden"}'='"address@hidden"'
+  setopt NO_GLOB_SUBST
 elif test -n "${BASH_VERSION+set}" && (set -o posix) >/dev/null 2>&1; then
   set -o posix
 fi