Obsolete Macros is configure.ac

[pete4abw]

While scrub does not mandate any particular version of autoconf, the current configuration generates numerous warnings with current versions of autoconf.

$ ./autogen.sh
Running aclocal ... 
Running libtoolize ... 
Running autoheader ... 
Running automake ... 
configure.ac:37: installing 'config/compile'
configure.ac:16: installing 'config/missing'
libscrub/Makefile.am: installing 'config/depcomp'
Running autoconf ... 
configure.ac:9: warning: The macro `AC_CANONICAL_SYSTEM' is obsolete.
configure.ac:9: You should run autoupdate.
./lib/autoconf/general.m4:2081: AC_CANONICAL_SYSTEM is expanded from...
configure.ac:9: the top level
configure.ac:18: warning: 'AM_CONFIG_HEADER': this macro is obsolete.
configure.ac:18: You should use the 'AC_CONFIG_HEADERS' macro instead.
./lib/autoconf/general.m4:2434: AC_DIAGNOSE is expanded from...
aclocal.m4:781: AM_CONFIG_HEADER is expanded from...
configure.ac:18: the top level
configure.ac:44: warning: The macro `AC_HEADER_STDC' is obsolete.
configure.ac:44: You should run autoupdate.
./lib/autoconf/headers.m4:704: AC_HEADER_STDC is expanded from...
configure.ac:44: the top level
configure.ac:59: warning: The macro `AC_PROG_LIBTOOL' is obsolete.
configure.ac:59: You should run autoupdate.
config/libtool.m4:100: AC_PROG_LIBTOOL is expanded from...
configure.ac:59: the top level
configure.ac:60: warning: The macro `AC_HELP_STRING' is obsolete.
configure.ac:60: You should run autoupdate.
./lib/autoconf/general.m4:204: AC_HELP_STRING is expanded from...
config/ac_pkgconfig.m4:3: AC_PKGCONFIG is expanded from...
configure.ac:60: the top level
configure.ac:93: warning: The macro `AC_HELP_STRING' is obsolete.
configure.ac:93: You should run autoupdate.
./lib/autoconf/general.m4:204: AC_HELP_STRING is expanded from...
config/libgcrypt.m4:30: AM_PATH_LIBGCRYPT is expanded from...
lib/m4sugar/m4sh.m4:699: AS_IF is expanded from...
configure.ac:93: the top level
Cleaning up ...
Now run ./configure to configure scrub for your environment.

Suggest setting AC_PREREQ([#.##]) and running autoupdate and check. (There are other issues with configure.ac, but those will be covered in another issue.) These warnings are not fatal, however.