[PATCH] Make zpty module work in the cygwin and msys2

[Peiyuan Song <squallatf@xxxxxxxxx>]

cygwin have /dev/ptmx, need defined `_GNU_SOURCE 1` to use it, but
configure check /dev/ptmx is usable only defined it for linux.

Another probleam is cygwin upstream have an issue
https://cygwin.com/pipermail/cygwin-developers/2021-January/012030.html,
because of that issue, movefd will broken the fd opened by
posix_openpt, so that we mast disable movefd in zpty until cygwin
fix that issue.
---
 Src/Modules/zpty.c | 2 ++
 configure.ac       | 2 +-
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/Src/Modules/zpty.c b/Src/Modules/zpty.c
index 45fd15ee0..eadb7ceac 100644
--- a/Src/Modules/zpty.c
+++ b/Src/Modules/zpty.c
@@ -428,6 +428,7 @@ newptycmd(char *nam, char *pname, char **args, int
echo, int nblock)
        mypid = 0; /* trick to ensure we _exit() */
        zexit(lastval, ZEXIT_NORMAL);
     }
+#ifndef __CYGWIN__
     master = movefd(master);
     if (master == -1) {
        zerrnam(nam, "cannot duplicate fd %d: %e", master, errno);
@@ -435,6 +436,7 @@ newptycmd(char *nam, char *pname, char **args, int
echo, int nblock)
        ineval = oineval;
        return 1;
     }
+#endif

     p = (Ptycmd) zalloc(sizeof(*p));

diff --git a/configure.ac b/configure.ac
index 549cae3d6..16dafac05 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2460,7 +2460,7 @@ if test x$ac_cv_have_dev_ptmx = xyes -o
x$ac_cv_func_posix_openpt = xyes && \
    test x$ac_cv_func_ptsname = xyes; then
    AC_CACHE_CHECK([if /dev/ptmx is usable],
    ac_cv_use_dev_ptmx,
-   [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#ifdef __linux
+   [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#if defined(__linux) ||
defined(__CYGWIN__)
 #define _GNU_SOURCE 1
 #endif
 #include <stdlib.h>
--
2.30.0.windows.1