This fixes #803

harden pkgconf installation setup

See merge request !74

Description: harden: autotools: pkgconf
 Harden the pkgconf(1) installation set up by linking at installation time a
 versionless pkgconf metadata file to the installed but versioned one.
 This allows one to write Makefile files that remain valid between upgrades.
 This is illustrated in doc/demos/cppextensions/Makefile by dropping the
 problematic PY3DOTVERSION (see graph-tool issue #802).
Origin: vendor, Debian
Author: Jerome Benoit <calculus@rezozer.net>
Last-Update: 2025-02-23

This fixes #801

This fixes a boost bug: https://github.com/boostorg/graph/issues/199

The fix will be part of the new boost release (> 1.87).

This fixes #771

This fixes #799

This fixes the performance regression reported in #797

m4/ax_boost_base: add riscv64 to 64bit arches

See merge request !73