Update ax_boost_base.m4 to version in progress: autoconf-archive/autoconf-archive#198
This is a temporary workaround for the problem in the 0.19.0 release;
please pull in the upstream version when ready (see #17010).
Tree-SHA512: ea8c4e895f5414cd307a9d809d2ec35fa8de6a733d8bf66080b67634d27cfb8b8f6256ca583a73e3ad899eebb42e6fc256ea693ae735624f968b34469c626586