warn-on-use: use instead of link-warning Each *.in.h file serves two purposes - provide enough self-contained content to serve as a replacement for the system header regardless of the user's compiler, and offer the developer the ability to detect any gnulib modules that might have been inadvertantly excluded. The former requires independence from config.h, and routes everything through a Makefile.am snippet that uses @@ substitution specific to the modules that were in use, with details learned at configure time. The latter works by poisoning anything that gnulib did not replace, but which the developer had natively available, explaining why their tests passed during development. Poisoning relies on gcc features, and requires manual triggering by adding -DGNULIB_POSIXCHECK to CFLAGS; it assumes that <config.h> is properly included. In fact, we do not want to use @@ substitution for HAVE_DECL_* during poisoning, because the warning is only relevant for the gnulib modules which were not included, and thus where the m4 macros to set proper @@ values have not been run. Furthermore, we only need to poison interfaces that already have a declaration; if something is not declared, then the developer wouldn't have been able to link, so their code won't be using the problematic interface in the first place. * modules/stdio (Depends-on, Makefile.am): Drop link-warning. * modules/unistd (Depends-on, Makefile.am): Likewise. * modules/arpa_inet (Depends-on): Replace link-warning with warn-on-use. (Makefile.am): Update rules accordingly. * modules/ctype (Depends-on, Makefile.am): Likewise. * modules/dirent (Depends-on, Makefile.am): Likewise. * modules/fcntl-h (Depends-on, Makefile.am): Likewise. * modules/inttypes (Depends-on, Makefile.am): Likewise. * modules/langinfo (Depends-on, Makefile.am): Likewise. * modules/locale (Depends-on, Makefile.am): Likewise. * modules/math (Depends-on, Makefile.am): Likewise. * modules/search (Depends-on, Makefile.am): Likewise. * modules/signal (Depends-on, Makefile.am): Likewise. * modules/spawn (Depends-on, Makefile.am): Likewise. * modules/stdlib (Depends-on, Makefile.am): Likewise. * modules/string (Depends-on, Makefile.am): Likewise. * modules/strings (Depends-on, Makefile.am): Likewise. * modules/sys_file (Depends-on, Makefile.am): Likewise. * modules/sys_ioctl (Depends-on, Makefile.am): Likewise. * modules/sys_select (Depends-on, Makefile.am): Likewise. * modules/sys_socket (Depends-on, Makefile.am): Likewise. * modules/sys_stat (Depends-on, Makefile.am): Likewise. * modules/sys_times (Depends-on, Makefile.am): Likewise. * modules/sys_utsname (Depends-on, Makefile.am): Likewise. * modules/wchar (Depends-on, Makefile.am): Likewise. * m4/arpa_inet_h.m4 (gl_HEADER_ARPA_INET): Check which functions should be poisoned. * m4/ctype.m4 (gl_CTYPE_H): Likewise. * m4/dirent_h.m4 (gl_DIRENT_H): Likewise. * m4/fcntl_h.m4 (gl_FCNTL_H): Likewise. * m4/inttypes.m4 (gl_INTTYPES_H): Likewise. * m4/langinfo_h.m4 (gl_LANGINFO_H): Likewise. * m4/locale_h.m4 (gl_LOCALE_H): Likewise. * m4/math_h.m4 (gl_MATH_H): Likewise. * m4/search_h.m4 (gl_SEARCH_H): Likewise. * m4/signal_h.m4 (gl_SIGNAL_H): Likewise. * m4/spawn_h.m4 (gl_SPAWN_H): Likewise. * m4/stdio_h.m4 (gl_STDIO_H): Likewise. * m4/stdlib_h.m4 (gl_STDLIB_H): Likewise. * m4/string_h.m4 (gl_HEADER_STRING_H_BODY): Likewise. * m4/strings_h.m4 (gl_HEADER_STRINGS_H_BODY): Likewise. * m4/sys_file_h.m4 (gl_HEADER_SYS_FILE_H_DEFAULTS): Likewise. * m4/sys_ioctl_h.m4 (gl_SYS_IOCTL_H): Likewise. * m4/sys_select_h.m4 (gl_HEADER_SYS_SELECT): Likewise. * m4/sys_socket_h.m4 (gl_HEADER_SYS_SOCKET): Likewise. * m4/sys_stat_h.m4 (gl_HEADER_SYS_STAT_H): Likewise. * m4/sys_times_h.m4 (gl_SYS_TIMES_H): Likewise. * m4/sys_utsname_h.m4 (gl_SYS_UTSNAME_H): Likewise. * m4/unistd_h.m4 (gl_UNISTD_H): Likewise. * m4/wchar.m4 (gl_WCHAR_H): Likewise. * lib/arpa_inet.in.h: Use _GL_WARN_ON_USE instead of GL_LINK_WARNING. * lib/ctype.in.h: Likewise. * lib/dirent.in.h: Likewise. * lib/fcntl.in.h: Likewise. * lib/inttypes.in.h: Likewise. * lib/langinfo.in.h: Likewise. * lib/locale.in.h: Likewise. * lib/math.in.h: Likewise. * lib/search.in.h: Likewise. * lib/signal.in.h: Likewise. * lib/spawn.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_times.in.h: Likewise. * lib/sys_utsname.in.h: Likewise. * lib/unistd.in.h: Likewise. * lib/wchar.in.h: Likewise. Signed-off-by: Eric Blake <ebb9@byu.net>