Allow multiple gnulib generated include files to be combined. * gnulib-tool (func_compute_include_guard_prefix): New function. (func_emit_lib_Makefile_am, func_emit_tests_Makefile_am): Resolve also ${gl_include_guard_prefix} references. (func_import, func_create_testdir): Invoke func_compute_include_guard_prefix. * lib/arpa_inet.in.h: Use the @GUARD_PREFIX@ placeholder. * lib/ctype.in.h: Likewise. * lib/dirent.in.h: Likewise. * lib/errno.in.h: Likewise. * lib/fcntl.in.h: Likewise. * lib/float.in.h: Likewise. * lib/getopt.in.h: Likewise. * lib/iconv.in.h: Likewise. * lib/langinfo.in.h: Likewise. * lib/locale.in.h: Likewise. * lib/math.in.h: Likewise. * lib/netdb.in.h: Likewise. * lib/netinet_in.in.h: Likewise. * lib/poll.in.h: Likewise. * lib/pthread.in.h: Likewise. * lib/pty.in.h: Likewise. * lib/sched.in.h: Likewise. * lib/se-selinux.in.h: Likewise. * lib/search.in.h: Likewise. * lib/signal.in.h: Likewise. * lib/spawn.in.h: Likewise. * lib/stdarg.in.h: Likewise. * lib/stddef.in.h: Likewise. * lib/stdint.in.h: Likewise. * lib/stdio.in.h: Likewise. * lib/stdlib.in.h: Likewise. * lib/string.in.h: Likewise. * lib/strings.in.h: Likewise. * lib/sys_file.in.h: Likewise. * lib/sys_ioctl.in.h: Likewise. * lib/sys_select.in.h: Likewise. * lib/sys_socket.in.h: Likewise. * lib/sys_stat.in.h: Likewise. * lib/sys_time.in.h: Likewise. * lib/sys_times.in.h: Likewise. * lib/sys_uio.in.h: Likewise. * lib/sys_utsname.in.h: Likewise. * lib/sys_wait.in.h: Likewise. * lib/sysexits.in.h: Likewise. * lib/termios.in.h: Likewise. * lib/time.in.h: Likewise. * lib/unistd.in.h: Likewise. * lib/wchar.in.h: Likewise. * lib/wctype.in.h: Likewise. * modules/arpa_inet (Makefile.am): Substitute @GUARD_PREFIX@. * modules/ctype (Makefile.am): Likewise. * modules/dirent (Makefile.am): Likewise. * modules/errno (Makefile.am): Likewise. * modules/fcntl-h (Makefile.am): Likewise. * modules/float (Makefile.am): Likewise. * modules/getopt-posix (Makefile.am): Likewise. * modules/iconv-h (Makefile.am): Likewise. * modules/langinfo (Makefile.am): Likewise. * modules/locale (Makefile.am): Likewise. * modules/math (Makefile.am): Likewise. * modules/netdb (Makefile.am): Likewise. * modules/netinet_in (Makefile.am): Likewise. * modules/poll-h (Makefile.am): Likewise. * modules/pthread (Makefile.am): Likewise. * modules/pty (Makefile.am): Likewise. * modules/sched (Makefile.am): Likewise. * modules/search (Makefile.am): Likewise. * modules/selinux-h (Makefile.am): Likewise. * modules/signal (Makefile.am): Likewise. * modules/spawn (Makefile.am): Likewise. * modules/stdarg (Makefile.am): Likewise. * modules/stddef (Makefile.am): Likewise. * modules/stdint (Makefile.am): Likewise. * modules/stdio (Makefile.am): Likewise. * modules/stdlib (Makefile.am): Likewise. * modules/string (Makefile.am): Likewise. * modules/strings (Makefile.am): Likewise. * modules/sys_file (Makefile.am): Likewise. * modules/sys_ioctl (Makefile.am): Likewise. * modules/sys_select (Makefile.am): Likewise. * modules/sys_socket (Makefile.am): Likewise. * modules/sys_stat (Makefile.am): Likewise. * modules/sys_time (Makefile.am): Likewise. * modules/sys_times (Makefile.am): Likewise. * modules/sys_uio (Makefile.am): Likewise. * modules/sys_utsname (Makefile.am): Likewise. * modules/sys_wait (Makefile.am): Likewise. * modules/sysexits (Makefile.am): Likewise. * modules/termios (Makefile.am): Likewise. * modules/time (Makefile.am): Likewise. * modules/unistd (Makefile.am): Likewise. * modules/wchar (Makefile.am): Likewise. * modules/wctype-h (Makefile.am): Likewise. * modules/assert-h (Makefile.am): Replace _GL_VERIFY_H specially.