Update configure.ac with autoupdate

[eerovaher]

pyerfa requires ERFA's config.h to be present. I tried to manually run the commands that the pyerfa setup.py file tries to run: https://github.com/liberfa/pyerfa/blob/88c25e6a125c4df2dadf0f969b8d626483722f62/setup.py#L126-L127
On current master I get

$ ./bootstrap.sh 
configure.ac:7: warning: The macro `AC_CONFIG_HEADER' is obsolete.
configure.ac:7: You should run autoupdate.
./lib/autoconf/status.m4:719: AC_CONFIG_HEADER is expanded from...
configure.ac:7: the top level
configure.ac:12: installing 'build-aux/compile'
configure.ac:10: installing 'build-aux/install-sh'
configure.ac:10: installing 'build-aux/missing'
src/Makefile.am:1: error: Libtool library used but 'LIBTOOL' is undefined
src/Makefile.am:1:   The usual way to define 'LIBTOOL' is to add 'LT_INIT'
src/Makefile.am:1:   to 'configure.ac' and run 'aclocal' and 'autoconf' again.
src/Makefile.am:1:   If 'LT_INIT' is in 'configure.ac', make sure
src/Makefile.am:1:   its definition is in aclocal's search path.
src/Makefile.am: installing 'build-aux/depcomp'
parallel-tests: installing 'build-aux/test-driver'
autoreconf: error: automake failed with exit status: 1

Following the instructions about running autoupdate produces

$ autoupdate
$ git diff
diff --git a/configure.ac b/configure.ac
index a3dc59b..70bbda8 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1,10 +1,10 @@
 # Process this file with autoconf to produce a configure script.
 
-AC_PREREQ([2.68])
+AC_PREREQ([2.71])
 ## Follow the instructions in RELEASE.rst to change package version
 AC_INIT([erfa],[2.0.1])
 AC_CONFIG_SRCDIR([src/erfa.h])
-AC_CONFIG_HEADER([config.h])
+AC_CONFIG_HEADERS([config.h])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_AUX_DIR([build-aux])
 AM_INIT_AUTOMAKE([foreign])

I did not see a need to update the requires version of autoconf, but I did check that AC_CONFIG_HEADERS is present in autoconf==2.68.
With this patch I no longer get the warning, but I still get

$ ./bootstrap.sh 
configure.ac:12: installing 'build-aux/compile'
configure.ac:10: installing 'build-aux/install-sh'
configure.ac:10: installing 'build-aux/missing'
src/Makefile.am:1: error: Libtool library used but 'LIBTOOL' is undefined
src/Makefile.am:1:   The usual way to define 'LIBTOOL' is to add 'LT_INIT'
src/Makefile.am:1:   to 'configure.ac' and run 'aclocal' and 'autoconf' again.
src/Makefile.am:1:   If 'LT_INIT' is in 'configure.ac', make sure
src/Makefile.am:1:   its definition is in aclocal's search path.
src/Makefile.am: installing 'build-aux/depcomp'
parallel-tests: installing 'build-aux/test-driver'
autoreconf: error: automake failed with exit status: 1
$ aclocal
$ autoconf
$ ./bootstrap.sh 
src/Makefile.am:1: error: Libtool library used but 'LIBTOOL' is undefined
src/Makefile.am:1:   The usual way to define 'LIBTOOL' is to add 'LT_INIT'
src/Makefile.am:1:   to 'configure.ac' and run 'aclocal' and 'autoconf' again.
src/Makefile.am:1:   If 'LT_INIT' is in 'configure.ac', make sure
src/Makefile.am:1:   its definition is in aclocal's search path.
autoreconf: error: automake failed with exit status: 1

I don't know how to solve that.

[mhvk]

Thanks! I indeed get the warning on master and not with this PR.

On my Debian/linux machine, I do not get the other problem you mentioned, about LIBTOOL. Maybe that is mac-specific?

Anyway, let's get this change in!

[eerovaher]

Installing libtool got rid of the error.

[mhvk]

Installing libtool got rid of the error.

Great!