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diff --git a/m4/host-os.m4 b/m4/host-os.m4
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+# serial 10
+
+# Copyright (C) 2001, 2003-2004, 2006, 2009-2018 Free Software Foundation, Inc.
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# Written by Paul Eggert.
+
+dnl From Paul Eggert.
+
+# Define HOST_OPERATING_SYSTEM to a name for the host operating system.
+AC_DEFUN([gl_HOST_OS],
+[
+  AC_REQUIRE([AC_CANONICAL_HOST])dnl
+  AC_CACHE_CHECK([host operating system],
+    [gl_cv_host_operating_system],
+
+    [[case $host_os in
+
+       # These operating system names do not use the default heuristic below.
+       # They are in reverse order, so that more-specific prefixes come first.
+       winnt*)          os='Windows NT';;
+       vos*)            os='VOS';;
+       sysv*)           os='Unix System V';;
+       superux*)        os='SUPER-UX';;
+       sunos*)          os='SunOS';;
+       stop*)           os='STOP';;
+       sco*)            os='SCO Unix';;
+       riscos*)         os='RISC OS';;
+       riscix*)         os='RISCiX';;
+       qnx*)            os='QNX';;
+       pw32*)           os='PW32';;
+       ptx*)            os='ptx';;
+       plan9*)          os='Plan 9';;
+       osf*)            os='Tru64';;
+       os2*)            os='OS/2';;
+       openbsd*)        os='OpenBSD';;
+       nsk*)            os='NonStop Kernel';;
+       nonstopux*)      os='NonStop-UX';;
+       netbsd*-gnu*)    os='GNU/NetBSD';; # NetBSD kernel+libc, GNU userland
+       netbsd*)         os='NetBSD';;
+       mirbsd*)         os='MirBSD';;
+       knetbsd*-gnu)    os='GNU/kNetBSD';; # NetBSD kernel, GNU libc+userland
+       kfreebsd*-gnu)   os='GNU/kFreeBSD';; # FreeBSD kernel, GNU libc+userland
+       msdosdjgpp*)     os='DJGPP';;
+       mpeix*)          os='MPE/iX';;
+       mint*)           os='MiNT';;
+       mingw*)          os='MinGW';;
+       lynxos*)         os='LynxOS';;
+       linux*)          os='GNU/Linux';;
+       hpux*)           os='HP-UX';;
+       hiux*)           os='HI-UX';;
+       gnu*)            os='GNU';;
+       freebsd*)        os='FreeBSD';;
+       dgux*)           os='DG/UX';;
+       bsdi*)           os='BSD/OS';;
+       bsd*)            os='BSD';;
+       beos*)           os='BeOS';;
+       aux*)            os='A/UX';;
+       atheos*)         os='AtheOS';;
+       amigaos*)        os='Amiga OS';;
+       aix*)            os='AIX';;
+
+       # The default heuristic takes the initial alphabetic string
+       # from $host_os, but capitalizes its first letter.
+       [A-Za-z]*)
+         os=`
+           expr "X$host_os" : 'X\([A-Za-z]\)' | LC_ALL=C tr '[a-z]' '[A-Z]'
+         ``
+           expr "X$host_os" : 'X.\([A-Za-z]*\)'
+         `
+         ;;
+
+       # If $host_os does not start with an alphabetic string, use it unchanged.
+       *)
+         os=$host_os;;
+     esac
+     gl_cv_host_operating_system=$os]])
+  AC_DEFINE_UNQUOTED([HOST_OPERATING_SYSTEM],
+    "$gl_cv_host_operating_system",
+    [The host operating system.])
+])