Use gnuconfig package for config file replacement for RISC-V. (#26364)

* 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.

lib/spack/external/__init__.py

@@ -11,7 +11,7 @@
 
 * Homepage: https://pypi.python.org/pypi/archspec
 * Usage: Labeling, comparison and detection of microarchitectures
-* Version: 0.1.2 (commit 8940a8b099a54ded21f8cf4314c4b83b558bb6d1)
+* Version: 0.1.2 (commit 85757b6666422fca86aa882a769bf78b0f992f54)
 
 argparse
 --------

lib/spack/external/archspec/README.md

@@ -49,6 +49,19 @@ $ tox
   congratulations :)
 ```
 
+## Citing Archspec
+
+If you are referencing `archspec` in a publication, please cite the following
+paper:
+
+ * Massimiliano Culpo, Gregory Becker, Carlos Eduardo Arango Gutierrez, Kenneth
+   Hoste, and Todd Gamblin.
+   [**`archspec`: A library for detecting, labeling, and reasoning about
+   microarchitectures**](https://tgamblin.github.io/pubs/archspec-canopie-hpc-2020.pdf).
+   In *2nd International Workshop on Containers and New Orchestration Paradigms
+   for Isolated Environments in HPC (CANOPIE-HPC'20)*, Online Event, November
+   12, 2020.
+
 ## License
 
 Archspec is distributed under the terms of both the MIT license and the

lib/spack/external/archspec/cpu/detect.py

@@ -306,3 +306,22 @@ def compatibility_check_for_aarch64(info, target):
         and (target.vendor == vendor or target.vendor == "generic")
         and target.features.issubset(features)
     )
+
+
+@compatibility_check(architecture_family="riscv64")
+def compatibility_check_for_riscv64(info, target):
+    """Compatibility check for riscv64 architectures."""
+    basename = "riscv64"
+    uarch = info.get("uarch")
+
+    # sifive unmatched board
+    if uarch == "sifive,u74-mc":
+        uarch = "u74mc"
+    # catch-all for unknown uarchs
+    else:
+        uarch = "riscv64"
+
+    arch_root = TARGETS[basename]
+    return (target == arch_root or arch_root in target.ancestors) and (
+        target == uarch or target.vendor == "generic"
+    )

lib/spack/external/archspec/json/cpu/microarchitectures.json

@@ -2017,6 +2017,44 @@
       "features": [],
       "compilers": {
       }
+    },
+    "riscv64": {
+      "from": [],
+      "vendor": "generic",
+      "features": [],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "7.1:",
+            "flags" : "-march=rv64gc"
+          }
+        ],
+        "clang": [
+          {
+            "versions": "9.0:",
+            "flags" : "-march=rv64gc"
+          }
+        ]
+      }
+    },
+    "u74mc": {
+      "from": ["riscv64"],
+      "vendor": "SiFive",
+      "features": [],
+      "compilers": {
+        "gcc": [
+          {
+            "versions": "10.2:",
+            "flags" : "-march=rv64gc -mtune=sifive-7-series"
+          }
+        ],
+        "clang" : [
+          {
+            "versions": "12.0:",
+            "flags" : "-march=rv64gc -mtune=sifive-7-series"
+          }
+        ]
+      }
     }
   },
   "feature_aliases": {