* Use gnuconfig package for config file replacement for RISC-V.
This extends the changes in #26035 to handle RISC-V. Before this change,
many packages fail to configure on riscv64 due to config.guess being too
old to know about RISC-V. This is seen out of the box when clingo fails
to build from source due to pkgconfig failing to configure, throwing
error: "configure: error: cannot guess build type; you must specify one".
* Add riscv64 architecture
* Update vendored archspec from upstream project.
These archspec updates include changes needed to support riscv64.
* Update archspec's __init__.py to reflect the commit hash of archspec being used.
