AM_PROG_AR error in ./prepare

[mtlam]

Running sudo ./prepare, I then saw:

libtoolize: putting auxiliary files in AC_CONFIG_AUX_DIR, 'config'.
libtoolize: copying file 'config/ltmain.sh'
libtoolize: putting macros in AC_CONFIG_MACRO_DIRS, 'config'.
libtoolize: copying file 'config/libtool.m4'
libtoolize: copying file 'config/ltoptions.m4'
libtoolize: copying file 'config/ltsugar.m4'
libtoolize: copying file 'config/ltversion.m4'
libtoolize: copying file 'config/lt~obsolete.m4'
configure.ac:7: installing 'config/compile'
configure.ac:5: installing 'config/missing'
automake: warnings are treated as errors
/usr/share/automake-1.15/am/ltlibrary.am: warning: 'libpsrfits_utils.la': linking libtool libraries using a non-POSIX
/usr/share/automake-1.15/am/ltlibrary.am: archiver requires 'AM_PROG_AR' in 'configure.ac'
Makefile.am:15: while processing Libtool library 'libpsrfits_utils.la'
Makefile.am: installing 'config/depcomp'
autoreconf: automake failed with exit status: 1

Thanks to google, I added AM_PROG_AR after AM_INIT_AUTOMAKE in configure.ac. I was then able to prepare, configure, and make without issues. Don't ask me why though.

[mtlam]

Shami sees the same issue on Mac OS X 10.14.5 (Mojave) with the same fix. I'm on Linux Mint 18.3.