link-warning: always build headers with link warnings

link-warning: always build headers with link warnings

Replacement headers must be built unconditionally if they use
GL_LINK_WARNING, if the warning is to ever trigger on a
glibc system during CFLAGS=-DGNULIB_POSIXCHECK.

* modules/arpa_inet (Makefile.am): Always build replacement
header.
* modules/ctype (Makefile.am): Likewise.
* modules/dirent (Makefile.am): Likewise.
* modules/inttypes (Makefile.am): Likewise.
* modules/langinfo (Makefile.am): Likewise.
* modules/locale (Makefile.am): Likewise.
* modules/spawn (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_times (Makefile.am): Likewise.
* modules/sys_utsname (Makefile.am): Likewise.
* modules/sys_wait (Makefile.am): Likewise.
* modules/wchar (Makefile.am): Likewise.
* m4/arpa_inet_h.m4 (gl_HEADER_ARPA_INET)
(gl_ARPA_INET_H_DEFAULTS): Drop unneeded variable.
* m4/ctype.m4 (gl_CTYPE_H_DEFAULTS): Likewise.
* m4/isblank.m4 (gl_FUNC_ISBLANK): Likewise.
* m4/dirent_h.m4 (gl_REPLACE_DIRENT_H, gl_DIRENT_H_DEFAULTS):
Likewise.
* m4/inttypes.m4 (gl_INTTYPES_H): Likewise.
* m4/langinfo_h.m4 (gl_LANGINFO_H): Likewise.
* m4/locale_h.m4 (gl_REPLACE_LOCALE_H, gl_LOCALE_H_DEFAULTS):
Likewise.
* m4/spawn_h.m4 (gl_REPLACE_SPAWN_H, gl_SPAWN_H_DEFAULTS):
Likewise.
* m4/sys_file_h.m4 (gl_HEADER_SYS_FILE_H): Likewise.
* m4/sys_ioctl_h.m4 (gl_SYS_IOCTL_H, gl_REPLACE_SYS_IOCTL_H)
(gl_SYS_IOCTL_H_DEFAULTS): Likewise.
* m4/sys_select_h.m4 (gl_HEADER_SYS_SELECT): Likewise.
* m4/sys_times_h.m4 (gl_SYS_TIMES_H): Likewise.
* m4/sys_utsname_h.m4 (gl_SYS_UTSNAME_H)
(gl_SYS_UTSNAME_H_DEFAULTS): Likewise.
* m4/wchar.m4 (gl_WCHAR_H, gl_REPLACE_WCHAR_H)
(gl_WCHAR_H_DEFAULTS): Likewise.