ASP-based solver: suppress warnings when constructing facts (#23090)

fixes #22786

Trying to get optimization flags for a specific target from
a compiler may trigger warnings. In the context of constructing
facts for the ASP-based solver we don't want to show these
warnings to the user, so here we simply ignore them.

lib/spack/spack/solver/asp.py

@@ -12,6 +12,7 @@
 import sys
 import time
 import types
+import warnings
 from six import string_types
 
 import archspec.cpu
@@ -1040,6 +1041,8 @@ def _supported_targets(self, compiler_name, compiler_version, targets):
 
         for target in targets:
             try:
+                with warnings.catch_warnings():
+                    warnings.simplefilter("ignore")
                     target.optimization_flags(compiler_name, compiler_version)
                 supported.append(target)
             except archspec.cpu.UnsupportedMicroarchitecture: