Pull in third-party poll emulator and automatically link it in if we detect the system's poll is broken

configure.ac

@@ -242,9 +242,63 @@ PKG_CHECK_MODULES([TINFO], [tinfo], ,
 
 AC_ARG_VAR([poll_CFLAGS], [C compiler flags for poll])
 AC_ARG_VAR([poll_LIBS], [linker flags for poll])
-if test -z "$poll_LIBS"; then
-   AC_CHECK_LIB([poll], [poll], [poll_LIBS="-lpoll"])
-fi
+AS_IF([test -z "$poll_LIBS"], [
+  AC_CHECK_LIB([poll], [poll], [poll_LIBS="-lpoll"])
+])
+
+# Check to make sure poll() can handle stdin and ptys
+AC_CACHE_CHECK([whether poll can handle ptys],
+               [ac_cv_poll_pty],
+[
+  save_CFLAGS="$CFLAGS"
+  save_LIBS="$LIBS"
+
+  AS_IF([test "x$poll_CFLAGS" != "x"],
+    [CFLAGS="$CFLAGS $poll_CFLAGS"])
+
+  AS_IF([test "x$poll_LIBS" != "x"],
+    [LIBS="$LIBS $poll_LIBS"])
+
+  AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <unistd.h>
+#include <stdio.h>
+#include <stdlib.h>
+#if HAVE_PTY_H
+#include <pty.h>
+#elif HAVE_UTIL_H
+#include <util.h>
+#endif
+#include <sys/poll.h>
+
+int master, slave;
+struct pollfd pollfds[ 1 ];
+]], [[
+if ( openpty( &master, &slave, NULL, NULL, NULL ) < 0 ) {
+   perror( "openpty" );
+   exit( 1 );
+}
+pollfds[ 0 ].fd = master;
+pollfds[ 0 ].events = POLLIN;
+int active_fds = poll( pollfds, 1, 100 );
+if ( active_fds < 0 ) {
+   perror( "poll" );
+   exit( 1 );
+}
+if ( pollfds[ 0 ].revents & (POLLERR | POLLHUP | POLLNVAL) ) {
+   exit( 2 );
+}
+]])],
+	[ac_cv_poll_pty=yes],
+	[ac_cv_poll_pty=no])
+  CFLAGS="$save_CFLAGS"
+  LIBS="$save_LIBS"
+])
+AM_CONDITIONAL([COND_THIRD_POLL], [test "x$ac_cv_poll_pty" = "xno"])
+AM_COND_IF([COND_THIRD_POLL],
+  [
+    poll_CFLAGS="-I\$(top_srcdir)/third/poll"
+    poll_LIBS="\$(top_builddir)/third/poll/libpoll.a"
+  ])
 
 AC_MSG_CHECKING([whether pipe2(..., O_CLOEXEC) is supported])
 AC_LINK_IFELSE([AC_LANG_PROGRAM([[#define _GNU_SOURCE
@@ -306,6 +360,7 @@ AC_CONFIG_FILES([
   Makefile
   third/Makefile
   third/libstddjb/Makefile
+  third/poll/Makefile
   src/Makefile
   src/crypto/Makefile
   src/frontend/Makefile