This avoids the following error when building under ubuntu 18.04
which has a never version of automake:
configure.ac:31: error: version mismatch. This is Automake 1.15.1,
configure.ac:31: but the definition used by this AM_INIT_AUTOMAKE
configure.ac:31: comes from Automake 1.15. You should recreate
configure.ac:31: aclocal.m4 with aclocal and run automake again.
