* acinclude.m4 (GNUPG_CHECK_ENDIAN): Use AC_COMPILE_IFELSE instead of
AC_TRY_COMPILE.  Use AC_RUN_IFELSE instead of AC_TRY_RUN.
(GNUPG_BUILD_PROGRAM): Use AS_HELP_STRING instead of AC_HELP_STRING.
* configure.ac: Use AC_USE_SYSTEM_EXTENSIONS instead of AC_GNU_SOURCE.
Use AS_HELP_STRING instead of AC_HELP_STRING.
(AC_ISC_POSIX): Replace by AC_SEARCH_LIBS.
(AC_TYPE_SIGNAL): Remove.
* m4/isc-posix.m4: Remove.
* m4/codeset.m4: Update from gnulib.
* m4/gettext.m4: Update from gnulib.
* m4/lcmessage.m4: Update from gnulib.
* m4/socklen.m4: Update from gnulib.
* m4/ldap.m4: Use AS_HELP_STRING instead of AC_HELP_STRING.
Use AC_LINK_IFELSE instead of AC_TRY_LINK.
Use AC_RUN_IFELSE instead of AC_TRY_RUN.
* m4/gpg-error.m4: Update from libgpg-error.
* m4/readline.m4: Update from libgpg-error.
* m4/npth.m4: Update from npth.
* m4/libassuan.m4: Update from libassuan.
* m4/libgcrypt.m4: Update from libgcrypt.
* m4/ksba.m4: Update from libksba.
* m4/ntbtls.m4: Update from ntbtls.
* common/signal.c [!HAVE_DOSISH_SYSTEM] (init_one_signal): Replace
RETSIGTYPE to void.
[!HAVE_DOSISH_SYSTEM] (got_fatal_signal, got_usr_signal): Likewise.