* configure.ac (AC_INIT): Use 'https://'.
Use AC_USE_SYSTEM_EXTENSIONS instead of AC_GNU_SOURCE.
(AC_ISC_POSIX): Replace by AC_SEARCH_LIBS.
Use AS_HELP_STRING instead of AC_HELP_STRING.
(AC_TYPE_SIGNAL): Remove.
(AC_DECL_SYS_SIGLIST): Remove.
* m4/ksba.m4: Update from libksba.
* m4/libgcrypt.m4: Update from libgcrypt.
* m4/libtool.m4: Update from libgpg-error.
* m4/gpg-error.m4: Update from libgpg-error.