use /dev/fd on Cygwin for process substitution

ChangeLog

@@ -1,3 +1,8 @@
+2020-01-10  Jun-ichi Takimoto  <takimoto-j@kba.biglobe.ne.jp>
+
+	* 45264: configure.ac: use /dev/fd on Cygwin for process
+	substitution
+
 2020-01-09  Daniel Shahaf  <danielsh@apache.org>
 
 	* unposted: Completion/Debian/Command/_sbuild,

configure.ac

@@ -2059,17 +2059,9 @@ dnl be good enough.
 AH_TEMPLATE([PATH_DEV_FD],
 [Define to the path of the /dev/fd filesystem.])
 AC_CACHE_CHECK(for /dev/fd filesystem, zsh_cv_sys_path_dev_fd,
-[if test "$host_os" = cygwin; then
-dnl In current (2008/12/01) versions of Cygwin these are present but don't
-dnl seem to work smoothly for process substitution; no great surprise
-dnl since getting processes to work at all on Cygwin is a big challenge.
-dnl We'll rely on FIFOs, since they do what we need.
-zsh_cv_sys_path_dev_fd=no
-else
 [for zsh_cv_sys_path_dev_fd in /proc/self/fd /dev/fd no; do
    test x`echo ok|(exec 3<&0; cat $zsh_cv_sys_path_dev_fd/3 2>/dev/null;)` = xok && break
- done]
-fi])
+ done])
 if test x$zsh_cv_sys_path_dev_fd != xno; then
   AC_DEFINE_UNQUOTED(PATH_DEV_FD, "$zsh_cv_sys_path_dev_fd")
 fi
@@ -2260,14 +2252,9 @@ dnl -----------
 dnl named FIFOs
 dnl -----------
 dnl
-dnl Named FIFOs work well enough on recent versions of Cygwin
-dnl to provide what we want.  Simply enable them.
 AC_CACHE_CHECK(if named FIFOs work,
 zsh_cv_sys_fifo,
-[if test "$host_os" = cygwin; then
-zsh_cv_sys_fifo=yes
-else
-AC_RUN_IFELSE([AC_LANG_SOURCE([[
+[AC_RUN_IFELSE([AC_LANG_SOURCE([[
 #include <fcntl.h>
 #include <signal.h>
 main()
@@ -2295,7 +2282,7 @@ main()
     exit(ret);
 }
 ]])],[zsh_cv_sys_fifo=yes],[zsh_cv_sys_fifo=no],[zsh_cv_sys_fifo=yes])
-fi])
+])
 AH_TEMPLATE([HAVE_FIFOS],
 [Define to 1 if system has working FIFOs.])
 if test x$zsh_cv_sys_fifo = xyes; then